Question

14. Tom had been studying French hard for nearly three years     he mastered it.

A. after       B. when

C. since      D. before

Answer 1

14.   D考查状语从句的连接词。句意："汤姆努力学了将近三年后才精通了法语"。before意为"在……之前;……之后， 才……；没来得及就……"。根据句意选D。