问题
填空题
人的性别是由______决定的．
答案
人体内每个细胞内有23对染色体．包括22对常染色体和一对性染色体．性染色体包括：X染色体和Y染色体．含有一对X染色体的受精卵发育成女性，而具有一条X染色体和一条Y染色体者则发育成男性．这样，对于女性来说，正常的性染色体组成是XX，男性是XY．
故答案为：性染色体
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人的性别是由______决定的．
人体内每个细胞内有23对染色体．包括22对常染色体和一对性染色体．性染色体包括：X染色体和Y染色体．含有一对X染色体的受精卵发育成女性，而具有一条X染色体和一条Y染色体者则发育成男性．这样，对于女性来说，正常的性染色体组成是XX，男性是XY．
故答案为：性染色体
| 阅读理解。 |
| It's a fine Sunday morning. Ann and her mother are in a big bus. There are many people in it. Some of them come from America, and some come from England and Canada. They are all their friends. They are going to the Great Wall. There are two Chinese in the bus. One is woman. She is driving the bus. The other is a young man. He speaks good English. He is now talking about the Great Wall. The other people are all listening to him. They like the Great Wall. They want to see it very much. |
| 1. Ann and mother are going to the Great Wall ______. |
[ ] |
| A. by bike B. by car C. by plane D. by bus |
| 2. There are ______. |
[ ] |
| A. only one Chinese in the bus B. only two Chinese in the bus C. only two Chinese on the bike D. only one Chinese in the car |
| 3. The driver is ______. |
[ ] |
| A. a man B. a woman C. a Canadian D. an American |
| 4. The people ______. |
[ ] |
| A. are singing B. are talking C. are listening D. are looking at the wall |
| 5. They ______. |
[ ] |
| A. can see the Great Wall B. can speak English very well. C. want to talk with the man very much D. want to see the Great Wall very much |