The experts in scientific problems are invited, and the experts in scientific problems are here

From the perspective of evolution, viviparity is superior, and the fertilization rate and survival rate of young fetuses are higher than oviparous.

However, viviparity takes longer for the mother to grow than the egg (although oviparity requires hatching).

Viviparous: mammals, bats, seals, fur seals, dolphins, baboons, pangolins, meerkats, anteaters, sea otters.

Viviparity: The fertilized egg develops within the mother's body, and nutrients come from the mother's body.

Oviparous: frogs, insects, reptiles, seahorses, platypus, rare moles.

Oviparous: A fertilized egg develops outside the mother's body and the nutrients come from the egg.

2) Courtship followed by mating, mating followed by childbirth. There are many ways of production, which are basically divided into oviparous, viviparous, and ovoviviparous.

For example, the eggs of some venomous snakes are always carried in the mother's belly, and the baby snake is hatched in the mother's womb before it is produced, because the nutrition of the baby snake comes from the egg rather than from the placenta, so it is called ovoviviparity.

Generally speaking, it is the job of females to give birth, although there are a few exceptions, and seahorses are one of them. Seahorses are wonderful fish, but they don't look like fish.

In addition, the female seahorse will place her eggs on the incubator on the male seahorse, and the male seahorse will be responsible for the work of pregnancy, so the baby seahorse is born from the mother's womb.

3) We know that most reptiles are oviparous, but some venomous snakes are ovoviviparous. The so-called ovoviviparity, that is, the fertilized egg is not excreted from the body like oviparous animals, and is hatched by the external environment, but remains in the mother's body and is produced after it develops into a small animal. This mode of reproduction looks very similar to viviparity, but when it develops in the mother's body, it is not nourished by the mother's ** like viviparous animals, and mainly depends on the nutrition of the fertilized egg itself, but the egg is "stored" in the mother's body to hatch, and it is still oviparous in essence.

Data 4) 1 oviparous. Oviparous animals excrete their eggs or fertilized eggs from their bodies, bury them in soil and sand (e.g., locusts, turtles, some snakes, etc.), or leave them in the bark of trees (e.g., cicadas), or in waters (e.g., fish, frogs, etc.), and then develop into larvae or larvae by the radiant heat of the sun.

2 viviparities. The fertilized eggs of ovoviviparous animals stay in the mother's reproductive tract, and develop into larvae through the vitelline of the egg itself, and when they mature, the mother's reproductive tract contracts to excrete the larvae and the vitelline membrane. Therefore, the embryos of ovoviviparous animals are properly protected by the mother, and the hatching survival rate is more secure than that of oviparous animals.

Oviviparous animals include some sharks, guppies, and pot-bellied fish.

3. Ovoviviparous. The fertilized eggs of viviparous animals are generally very small and have little vitelline. Fertilization is completed at the upper end of the mother's fallopian tube, then develops into an early embryo, descends to the uterus, and then buries it in the inner wall of the mother's uterus, where it is connected to the mother through the placenta to absorb nutrients and oxygen from the mother's blood, and deliver carbon dioxide and waste products to the mother's blood for elimination.

When the fetus matures, uterine contractions expel the larvae from the body, forming a new life of its own. Among the mammals, except for the platypus and echidna, which are oviparous, the others are viviparous.

I also looked for it from above).

The fundamental difference is whether there are eggs or not; Both ways have their own merits!

1 is not a uniform linear motion. Because the recording time is uneven.

2 Known, 30km 7:05, 40km 7:25, 50km 7:39.

Find 50km-20km=30km

7:39-6:45=54 (min).

30km÷54min×60min=

Abbreviated here. It's ugly.

Solution 1: It is not a uniform motion, the reason: the first section: 15 minutes 10 kilometers, the second stage: 20 minutes 10 kilometers.

After 30 km, the car travels s=s1 (10 km) + s2 (50 m) =;

3)s/t=；

4) A: The average speed of the car in the last 30 kilometers is.

H2SO4 + 2NaOH = Na2SO4 + H2OCUSO4 + 2NaOH = Na2SO4 + Cu(OH) 100g 40% NaOH solution contains 40g of sodium hydroxide, which is 1mol 50g solution contains 20g, for.

When 50g is not precipitated, it means that it has not reacted with CuSO4.

Substituting the chemical equation can be calculated as sulfuric acid and the mass is .

The concentration of sulfuric acid is:

Due to the reaction with sulfuric acid, then only the reaction with copper sulfate, the copper hydroxide precipitated is, the mass is after the reaction, 100g of sodium hydroxide is added, and the precipitate is generated, so the total solution mass is 200+ The generated Na2SO4 is, (reacts with sulfuric acid and copper sulfate to form each, and the mass fraction is: 71

a.Hydrochloric acid: 2HCl + Ca(OH)2==CaCl2+2H2O (no color, gas, precipitation in the reaction).

b.Ferric chloride solution: 2FeCl3 + 3Ca(OH)2==2Fe(OH)3 +3CaCl2 (reddish-brown flocculent precipitate appears).

c.Copper sulfate solution: CuSO4 + Ca(OH)2==Cu(OH)2 + CaSO4 (blue flocculent precipitate appears).

d.Phenolphthalein solution: The main component of lime water is calcium hydroxide, which is alkaline, and the phenolphthalein test solution is red when alkaline.

The correct answer should be A

AhCl + Ca(Oh)2 CaCl2 + H2O limestone is originally clear, this reaction does not produce precipitation, and no gas is released to form Fe(Oh)3

c generates Cu(OH)2

dPhenolphthalein discoloration.

Lime water is calcium hydroxide, and the analysis is as follows:

There is no precipitation of gas, that is, there is no obvious phenomenon;

Iron hydroxide is a reddish-brown flocculent precipitate;

Copper hydroxide is a blue precipitate;

d.Lime water is a strong alkali, and phenolphthalein turns red when exposed to alkali.

Only A is eligible

I worked on chemistry for a long time.

Answer: AA: Ca(OH)2+2HCl=CaCl2+2H2O, no obvious phenomenon B: 2FeCl3+3Ca(OH)2=2Fe(OH)3 +3CaCl2, reddish-brown precipitate.

C: CuSO4+Ca(OH)2=Cu(OH)2+CaSO4, blue precipitate.

d: Phenolphthalein turns red when exposed to alkali.

The main component of lime water is calcium hydroxide, which reacts with iron chloride solution to form iron hydroxide precipitation. It is a phenomenon with copper sulfate solution to generate copper hydroxide precipitation. Because calcium hydroxide is alkaline and turns red when phenolphthalein, there is a phenomenon, so choose A

1. The quartz clock hanging on the wall wall often stops at the position of "9" on the dial when the battery is exhausted and stops moving. This is due to the fact that the second hand is most hindered by the gravitational moment at the "9" position.

2. Sometimes when the water pipe discharges water from the adjacent faucet, there is an occasional burst of noise. This is due to the resonance of the water pipes caused by the water flushing out of the faucet.

3. When taking pictures of the TV screen, the camera flash and indoor lighting should be turned off, so that the ** picture is clearer. Because the reflected light from the flash and the light on the electric guess screen can interfere with the transmitted light of the TV picture

4. Frozen* meat thaws faster in water than in air at the same temperature. Boiling nails cool down faster in water than in air at the same temperature. A cup filled with piping hot boiling water cools down faster when immersed in water than in air at the same temperature.

All these phenomena show that the heat transfer of water is better than that of air

This is a question of observation and inspection, but you didn't observe it, so you had to come from the angle of the sun's elevation, I wonder if you have learned it?

The solar altitude angle is calculated as the absolute value of the 90° latitude difference.

The point of direct sunlight moves about a day and 10 days.

Let's say you choose the 15th of July, and measure it with a pole one meter long at 12 noon.

Their direct sun exposure points are respectively Tanqiao.

Their noon solar elevation angles are ., respectively3°

So: the length of the shadow is ., respectively38

The direct point of the sun or the area north of Wood is due south at noon.

If it helps, it will be supported in a timely manner

1, b, you can use the proportion, so, grinding x=

2. C3, there is friction on the cover of toothpaste, friction on the sole of the shoe, and friction on the bottom of the tire.

4. Soak in water, dip the key and there are bubbles.

5. Prevent slipping.

6. Vertical placement.

7. Lions eat antelopes and zebras, which is a normal food chain and can maintain ecological balance.

m, c car potato Ming uses Sun Bi snow chains, bicycle handbrake, and wears spiked shoes.

Not. If you increase the friction, you will have a hand-to-hand force.

Not. Biological chain balance.

BC bikes use snow chains, bicycle handbrakes, and spiked shoes.

Not. Increase friction for land bridges.

Not. Biological chain splitting and balancing.

The degree of scalding of the human body by water vapor of the same mass of 100 degrees Celsius is much greater than that of the human body burned by boiling water at 100 degrees Celsius. The reason for this is (water vapor liquefies into water, and a lot of heat is released).

Splash a few drops into a hot, dry iron pot and you can see the droplets bounce irregularly along the walls of the pot until the pure water droplets disappear. How can this phenomenon be explained?

Because of the large amount of water vapor generated, these water vapors drop water'Blow'It has to beat irregularly.

1.Because the liquefaction of water vapor into water will emit a lot of heat.

2.Boiling to sublimation.

1) Liquefaction of water vapor at 100 degrees into water requires the release of a large amount of heat.

2) irregular movement by heat; Gasification phenomenon.