问题 选择题

从单个细胞来看,人体下列哪种细胞内染色体数目最多(  )

A.成熟的红细胞

B.成熟的卵细胞

C.精子细胞

D.白细胞

答案

生物体的细胞内有一些被碱性染料染成深色的物质,叫做染色体.染色体在生物体的传宗接代中,具有重要的作用.在生殖过程中,要进行一种特殊方式的细胞分裂,结果使生殖细胞中的染色体的数量减少一半.人体产生的精子、卵细胞和受精卵的染色体数目分别是23条、23条、46条;白细胞是体细胞,其染色体是生殖细胞的二倍;红细胞是体细胞,但是成熟的红细胞没有细胞核,而染色体位于细胞核内,因此红细胞没有染色体,故含染色体数目最多的是白细胞.

故选D.

阅读理解

I receive many letters from children and can’t answer them all – there wouldn’t be enough time in a day. I’ll try to answer some of the questions that are commonly asked.

Where did I get the idea for Stuart Little and for Charlotte’s Web? Well, many years ago, I went to bed one night in a railway sleeping car, and during the night I dreamed about a tiny boy who acted rather like a mouse. That’s how the story of Stuart Little got started.

As for Charlotte’s Web, I like animals and my farm is very pleasant place to be – at all hours. One day, when I was on my way to feed the pig, I began feeling sorry for the pig because, like most pigs, he was going to die. This made me sad. So I started thinking of ways to save his life. Three years after I started writing it, it was published. (I am not a fast worker, as you can see.)

Sometimes I’m asked when I started to write, and what made me want to write. I started early – as soon as I could spell. Children often find pleasure through trying to set their thoughts down on paper, either in words or in pictures. I was not good at drawing, so I used words instead. As I grew older, I found that writing could be a way of earning a living.

Well, here is the answer to the last question. No, they are imaginary (虚构的) tales. In real life, a family doesn’t have a child who looks like a mouse and a spider doesn’t write words in her web. Although my stories are imaginary, I like to think that there is some truth in them, too – truth about the way people and animals feel, think and act.

小题1:E.B. White wrote this passage to ______.

A. introduce his new books

B. introduce two funny stories

C. explain why he enjoys writing

D. answer some readers’ questions

小题2:We can know from the passage that E.B. White is a writer who ______.

A. writes very fast

B. works on a friends’ farm

C. mainly writes stories for adults

D. writes imaginary tales for children

小题3:What inspired E.B. White to write Charlotte’s Web?

A. That he wanted children to love animals.

B. That he was deeply impressed by a clever pig.

C. That he wanted to use his own way to save a pig.

D. That he wanted to save the animals on a farm.

小题4: E.B. White started to write because he wanted to ______.

A. improve his spelling

B. express his thoughts

C. show his sadness

D. make a good living

小题5:What is probably the last question?

A.Are your stories true?

B.What is the truth in your stories?

C.Will you write more imaginary tales?

D.Do you know a child looking like a mouse?

填空题