4. If you miss this chance, it may be years ____ you get another one.
A
As
B
before
C
since
D
after
as引导的句子谓语动词只能延续性的,since引导的句子要用一般过去时态,after是“在什么之后”的意思,不符合逻辑,故选before。
理解句意并掌握状语从句的基本用法。
状语从句的用法和差异。