2. 外语
  3. We all scream for water【C1】______thirsty. But do you know in very hot, dry weather, plants also make faint sounds —【C2】______the

We all scream for water【C1】______thirsty. But do you know in very hot, dry weather, plants also make faint sounds —【C2】______the

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问题     We all scream for water【C1】______thirsty. But do you know in very hot, dry weather, plants also make faint sounds —【C2】______they are crying out for help?
    You see, in a plant’s stem, there are hundreds of water pipes that bring water and minerals from the soil【C3】______up to the leaves.【C4】______the ground turns dry, it becomes harder and harder for the plants to do this. In【C5】______droughts, plants have to fight to【C6】______any water available. Scientist Robert Winter has found out that when it is really bad, their water pipes【C7】______from the【C8】______like rubber bands. When that happens, the whole plant vibrates a little. The snapping pipes make noises【C9】______than a whisper. Robert knows that healthy, 【C10】______plants are quiet. He also knows that many insects prefer attacking【C11】______plants【C12】______healthy plants.
    How do the insects know which are healthy plants and which are not? Robert thinks that the insects may listen for the plants that cry. And then they【C13】______buzz in to kill. To【C14】______his theory, Robert is using a【C15】______that can【C16】______plant cries. He attaches it【C17】______a quiet, healthy plant so the plant sounds thirsty. Then he watches the insects to see if they attack more often than usual. If he is right, scientists could use the insects’ ability【C18】______them. They could build traps that imitate crying plants,【C19】______when the insects buzz in to eat, they won’t buzz【C20】______
【C1】
选项 A、when we
B、when are
C、when be
D、when
答案D
解析 语法辨析题。在状语从句中，当主句和从句的主语一致时，从句主语可以省略，变成非谓动词形式，从句谓语是be动词时可连同主语一起省略。本句中when后的主语we及动词are都省去了，完整句型为We all scream for water when we are thirsty．
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