题目内容：
根据短文，回答题。
From this passage, we can learn that__________ 。
A．a robotic caterpillar can crawl by a pair of rubber rods
B．when a caterpillar moves, the magnetic field moves backwards along it
C．the environment couldn't influence a robotic caterpillar's guts, which are wrapped in a capsule
D．crawling is very stable and efficient, and when it moves, only a few elements are needed
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答案解析：