题干

下图为精原细胞增殖以及形成精子过程示意图。图中标明了部分染色 体与染色体上的基因。设①③细胞都处于染色体的着丝点向两极移动的时期。下列关于图解叙述正确的是

A:②有姐妹染色单体,①③也可能有姐妹染色单体

B:②中有同源染色体,染色体数目为2n,DNA数目为4a

C:③中无同源染色体,染色体数目为n,DNA数目为2a

D:①中有同源染色体,染色体数目为2n,DNA数目为4a

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答案(点此获取答案解析)

B

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       Doctor Seuss was born in 1904. By the middle 1950s, he had become one of the best-loved and most successful children's book writers in the world. His books are very popular with young readers. They enjoy the invented words and the pictures of unusual funny animals and plants.

In l954, Life Magazine published(刊登) a report about school children who could not read. The report said many children's books were not interesting. Doctor Seuss strongly hoped to help children and decided to write books that were interesting and easy to read. He used words with the same ending sound, like fish and wish. He did not receive training in art. Yet, he drew the pictures for most of his books.

    In l957, Doctor Seuss wrote The Cat in the Hat. He used less than 230 words to write the book and even a six-year-old should be able to read it. It was a fun stow and easy to read. Children loved it. Their parents loved it, too. Today it is still one of his stories they like best. In l 960, he wrote a book using less than fifty words. The book is called Green Eggs and Ham.

    In l984, Doctor Seuss won a Pulitzer Prize(普利策奖). He was honored for the education and enjoyment his books provided American children and their parents.

    He died at the age of 87, but his influence remains. Millions of his books have been sold worldwide. People say his books helped change the way American children learned to read. Yet, his books are loved by people of all ages.