题干

将新鲜马铃薯切成粗细相同的5cm长条,再将它们分别放在浓度不同的甘露醇溶液中,4h后测量每条的长度,结果如图所示。以下有关分析正确的是( )

①马铃薯细胞液的浓度约为30g·L-1;
②当溶液浓度为40g·L-1时,细胞开始发生质壁分离;
③在溶液浓度为30g·L-1~90g·L-1的范围内,细胞壁也有一定程度的收缩;
在溶液浓度为20g·L-1,细胞能发生质壁分离。

A:②

B:③

C:①③

D:②④

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答案(点此获取答案解析)

C

同类题3

通读下面短文,掌握其大意,然后在每小题所给的四个选项中,选出一个最佳答案。

    My six-year-old granddaughter, Cindy, and I stopped at a food shop for some bread. Cindy had1 it for several days. As we were going out of the door, a young teenage boy was coming in.

    The boy had no hair on the side of his head but a set of blue spiked(成锥形的) hair on top of it. His nose was 2 , and a ring ran through the hole. A chain went across his face and it was connected to his earring. He held a skateboard under one arm and a basketball under the other.

    Cindy, who was walking ahead of me, 3stopped when he saw the boy. I thought he had  4 my granddaughter. I was wrong. My granddaughter backed up against the door and opened it as wide as it would go. Now I came face to face with the young man. I stepped aside and let him5. He replied very6, "Thank you very much."

    On our way to the car, I 7 Cindy for holding open the door for the boy. To my surprise, she didn't seem to be troubled by the young boy's 8 . But I wanted to make sure. I wanted to be ready to talk about freedom of expressing themselves and allowing people's  9   .

    As it turned out, the person  10needed the talk was me. The only thing Cindy noticed about the boy was the fact that his arms were   11 . "He held a skateboard under one arm and a basketball under the other. He would have a 12  time to open the door, " said Cindy.

    I just paid attention to the partially shaved (部分剃光的)head, the set of spiked hair, the piercing and the chain. She saw a person carrying   13 under each arm and heading toward a(n) 14 door.

    What my granddaughter said reminded me that I should change my ways of judging people and 15 my granddaughter to be open-minded and warm-hearted.