单选题 After people have learned that magnets attract things, centuries passed ______ they took note of the fact that magnets sometimes also repel things.
A. before B. until
C. after D. since

【正确答案】 A
【答案解析】[解析] 直译为：“在他们注意到……这一事实之前已经过了几百年，也就是说，几百年以后才……”全句可译为：“人们早已知道了磁体能吸引别的物体，又过了几百年，才注意到磁体有时也排斥别的物体这一事实。”