听力原文： A number of insects rely on leaping or jumping as a way of escaping from enemies. Grasshoppers probably have the most remarkable jumping ability of all these insects. If we think of it in human terms, a grasshopper's high jump is like a human jumping over a five story building. Imagine that a person jumping over a five story building. Welt, we'll take a look at the structure of grasshopper's leg to see why it's able to jump so well, but first I wanna talk about the sensory organ that tells grasshoppers when to jump in the first place. En, OK, a grasshopper has two sensory organs located at the end of its abdomen. Whenever these organs sense of change in air pressure which might be produced by an enemy approaching, an impulse is transmitted to the legs, this first impulse deactivates the nerves that control normal working and sets the grasshopper's jumping muscles into a sort of pre-jumping position. Now at this point, if the sensory organs don't detect additional air pressure changes, the jumping muscles relax and a grasshopper goes back to its normal walking. But if the organs continue to send danger, another set of impulses put the jumping muscles in motion. The distance of the jumping is determined by just how many impulses are transmitted in the second set, the more impulses the longer the jump. OK now let's see why the grasshopper can jump so far.
Whet does the professor mainly discuss?
A．How grasshoppers find food.
B．How grasshoppers fight other insects.
C．How grasshoppers communicate with each other.
D．How grasshoppers escape from danger.

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Whet
B.How
C.
B．How
D.
C．How
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D．How
F.