问题 选择题

海龟中有连趾(ww)和分趾(WW、Ww)两种类型,开始时,连趾(w)和分趾(W)的基因频率分别为0.4和0.6。当海龟数量增加导致食物不足时,连趾的海龟更容易从海水中得到食物。若干万年后,基因频率变化成W为0.2,w为0.8。下列有关说法正确的是[ ]

A.海龟基因频率的改变,是因为缺少食物的特殊环境使之产生了定向变异

B.海龟受环境影响而产生的变异都是不能遗传的

C.海龟基因频率的改变,说明海龟在自然选择的作用下发生了定向的进化

D.海龟基因频率已发生了很大变化,说明海龟已经进化形成一个新的物种

答案

答案:C

阅读理解

阅读理解

     There are 47 different kinds of kangaroos. The smallest is about a quarter of one meter long;

the biggest is taller than a man.

     Kangaroos have very long back legs. The legs are used for jumping. They also have long tails

used for resting on. Kangaroos' front legs are much shorter, and are almost like arms. Their heads

are quite small, but their ears are quite big.

     Mother kangaroos have a pocket(口袋)  at the front. They have one baby each year. When it

is born, the baby kangaroo goes straight into its mother's pocket. The baby kangaroo stays there

for six months.

     The biggest kangaroos stand more than 2 meters tall, and their back legs are so strong that they

can jump more than 9 meters. They can run at more than 50 kilometers per hour. They are very

strong, but only eat fruit, leaves and grass.

1. How many different kinds of kangaroos are there?

A. Seven.

B. Seventy-four.

C. Forty-seven.

D. Forty.

2. How large is the biggest kangaroo?

A. Smaller than a man.

B. Bigger than a man.

C. The same size as a man.

D. A quarter of one meter long.

3. Which of the following is TRUE?

A. All the kangaroos have a pocket.

B. Only baby kangaroos have a pocket.

C. Only mother kangaroos have a pocket.

D. All the above.

4. A baby kangaroo stays __________ in its mother's pocket.

A. one month

B. three months

C. six months

D. five months

5. Which of the following is TRUE about a kangaroo?

A.It has lots of babies each year.

B. It can rest on its tail.

C. It has four long legs.

D. It can't run very fast.

单项选择题