It was 2 months _____the young man mastered the skill of running the machine introduced from Korea.
问题描述：
It was 2 months _____the young man mastered the skill of running the machine introduced from Korea.
1since 2 before
2对
翻译
答
选2,before.因为第一按照语境句子所表达的意思,只能选before.它的意思是：两个月以前,这个年轻人掌握了一门从韩国引进的机器的操作技能.第二,since一般都要和完成时态连用,后面跟一个时间状语从句.