After people have learned that magnets attract things, centuries passed ______ they took note of the fact that magnets sometimes

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问题 After people have learned that magnets attract things, centuries passed ______ they took note of the fact that magnets sometimes also repel things.

选项 A、before
B、until
C、after
D、since

答案A

解析 before应该理解成“(几百年过去了,人们)才……”;如果用after应该是...after centuries passed they took note of the fact...;如果用until,应该是they didn’t take note of the fact that...until centuries passed.
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