语法与词汇 After people have learned that magnets attract things, centuries passed _____ they took note of the fact thatmagnets sometimes also repel things.
【正确答案】 A
【答案解析】句意：人们发现磁铁能吸引事物之后过了好几个世纪才发现有时磁铁也排斥事物。这里指的是人们发现磁铁能吸引事物以前过了好几个世纪，所以用before。