Seven biology double choice exercises, more points, and a reward for answering within 10 minutes, is

(4) Short-stem rice is not conducive to competition for light, low photosynthesis, and low yield. Therefore, it is not good.

2）.Short-legged healthy sheep.

Due to its short legs, it cannot jump over the fence of the sheepfold, so it is easy to keep in captivity. Therefore it is advantageous.

In 791, a peasant race in New England was copied in the United States.

Raid Si Huaibai

In the flock of Seth Wright's family, a male sheep with a long back and short legs and a slight curve was found. Due to its short legs, it cannot jump over the fence of the sheepfold, so it is easy to keep in captivity. After White's careful breeding, a new breed of sheep was born, the Ancon sheep.

Darwin was so intrigued by this that he included the example in his book Variations in Animals and Plants in Domestic Breeding. But the Ankang sheep became extinct around 1870. This short-legged sheep was initially caused by genetic changes in the germ cells of its parents.

A change in a gene is called a gene mutation. Around 1920, a short-legged sheep suddenly appeared in a Norwegian farmer's flock, due to a new genetic mutation. This led to the creation of a new breed of short-legged sheep.

This is the information of the short-legged Ankang sheep. Just take a look at it and you'll understand.

As the name suggests, the short-legged Ankang sheep has short legs, and it can't jump over the sheepfold fence, so it is easy to keep in captivity, so it is a favorable variation. Short-stem rice is not conducive to photosynthesis in rice.

Due to its short legs, the short-legged Ankang sheep cannot jump over the fence of the sheepfold, so it is easy to keep in captivity, so it is a mutation in our favor for humans. Rice is planted in water, and short-stem rice is easily flooded by water, resulting in death, so it is an unfavorable variation (for reference).

Ecosystems include biotic factors and abiotic environments.

In this question, B and D have only biological factors and no non-living factors, so B and D do not belong to ecosystems.

A and c have both biotic and abiotic environmental factors.

Therefore, the correct options for this question are A and C.

One:1(cerebral cortex).(140)

2.(4).(cerebellum).(3).(Brain).

3.(cerebral cortex).

II: 1(cerebral cortex).

2.(cerebellum).

3.Because the brainstem is in the back of the head. There are parts of the brain stem that regulate basic human activities such as heartbeat, breathing, and blood pressure. If these parts are damaged, the heartbeat and breathing stop, which can be life-threatening.

4.Wear a helmet.

1) Inspiratory dilation increases.

2) Decrease. 3) b Equal.

The answer is: a, d.

a, only in the small intestine does it contain enzymes that digest all three major nutrients;

B false, for saliva, can decompose starch into maltose, can not decompose into glucose;

C is false, the figure indicates that under the action of the enzyme, the fat is decomposed and then absorbed, so it should contain lipase;

d correct.