题干

如图是描述生命现象的模型(部分),以下相关叙述正确的是(    )

A:若A代表人体记忆B淋巴细胞,a为抗原刺激,则b、c可分别代表 B细胞和记忆细胞的形成

B:若A代表人体下丘脑,a为性激素,则b、c可分别代表促性腺激素和生长激素

C:若A代表棉铃虫种群,a为诱捕雄虫,则b、c可分别代表性别比例失调和种群密度降低

D:若A代表草原,a为过度放牧,则b、c可分别代表土地荒漠化和生物多样性提高

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C

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    Every day, a homeowner in Pennsylvania is reminded of a mistake he made 13 years ago. At around 8 in the evening, his peaceful house comes alive with the noise of an alarm clock he dropped into the wall over ten years ago. It's been stuck in the wall ever since.

    13 years ago, Jerry Lynn wanted to make a hole through his living room wall, so he could pass the television cable (电缆)through it. He didn't want to destroy any pipes in the wall, so he came up with a good idea to make sure that he was drilling(钻孔) in an empty place. He took his alarm clock, tied it to a string(线) and set it to go off in 10 minutes. Then he lowered it into the wall, and waited for it to ring. His goal was to drill a hole in a safe place near the place where the ringing was coming from, making sure that there was nothing to pass through there. It all went smoothly until the alarm clock fell into the wall.

The man didn't get back the alarm clock, but thought it would probably run out of battery(电池)in several months, so he wasn't too worried about it. But 13 years later, the alarm clock still rings every day.

    As you can imagine, Jerry and his wife have gotten used to the ringing living room wall, but it can still surprise  guests. So Jerry decides to pull down that wall, just to stop that boring thing, though after putting up with it for 13 years, he think it will be a pity. He says, “I've never herd of a clock battery lasting that long and my friends think it may be interesting to see how long it will keep ringing for.”