语法与词汇
After people have learned that magnets attract things, centuries passed_____ they took note of the fact that magnets sometimes also repel things.
【正确答案】
A
【答案解析】句意：在人们了解到磁铁吸引东西之后，几百年过去了，他们才注意到磁铁有时也会排斥物体。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”。since没有此用法。因此，本题的正确答案为A。