题干

下图表示利用二倍体西瓜(2N)培育出三倍体无子西瓜(3N)过程中染色体数目变化的情况,下列说法不正确的是(   )

A:①过程中染色体复制两次细胞分裂一次

B:②过程可能产生突变和基因重组

C:图中只包含有两个不同的物种

D:三倍体无子西瓜可能产生极少量可育的配子

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答案(点此获取答案解析)

A

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    Mrs. Brown was tired after her day's shopping in London, so she went into a restaurant for a cup of tea 1 catching the train home. When she had ordered her tea, she suddenly remembered that she had to buy some 2 for her husband, who had a cough.

    “Is there a chemist's near here?” she asked the waiter. “Yes, madam.” the waiter said. “It's only about three minutes' walk away. Turn right when you go out of the restaurant, then take the second turning to the left. You'll find a big chemist's about a hundred yards up the road on the right-hand side. It closes at five, but if you 3, you'll just get there in time.”

    Mrs. Brown followed the waiter's directions 4 and found the chemist's shop without any difficulty. She bought the cough mixture and started to 5 her way back to the restaurant. But after she had walked for about ten minutes and there was still no 6 of the restaurant, she realized that she must have made a mistake.

    “Oh! I am 7!” said Mrs. Brown. “I've left all my shopping in the restaurant and now I'm lost.”

    She was still wondering what to do when a policeman came 8 and asked if he could help. Mrs. Brown 9 what had happened.

    “Well, first of all,” said the policeman, “we had better go back as far as the chemist's”. “Now,” suggested the policeman, when they got to the chemist's, “let's go in this direction. It leads to the main road, where we shall probably find your restaurant.” When they reached the main road, the policeman said, “I think you'll find the restaurant you are looking for along there, on the opposite side of the road.” Mrs. Brown thanked the policeman for his help. “I can't 10 how I went wrong,” she said. The policeman smiled. “It's quite easy,” he said, “to get lost in a big city like London.”