Tom had been studying French hard for nearly three years he mastered it．A．afterB
来源：网络
时间：
推荐文章
Tom had been studying French hard for nearly three years he mastered it．
| A．after | B．when | C．since | D．before |
试题答案
D
解析试题分析:句意：——汤姆努力学了将近三年后才精通了法语。A在……之后；B当……时；C自从；D在……之前。根据前后句时态可知“学习法语”发生在“掌握法语”之前，所以用before，答案选D。
考点：考查连词用法。