Question

She _____ as a nurse in a hospital since three years ago.

A. works    B. worked    C. has worked    D. will work

Answer

C

【解析】句意：她从三年前就在一家医院当护士。since three years ago表示的是截止到目前为止的时间段，用于现在完成时态的句子中，故答案为C。

点睛：since的用法：译作“自从…以来”，(1)接时间点：如 I have stayed in that country since 1995. 要求：谓v.用现在完成时，而且须是延续性动词。(2)接一段时间 + ago：如 They have lived in that house since two years ago. 要求：谓v.用现在完成时，而且须是延续性动词。(3)接时间状语从句：如 I have loved her since I met her last time. / Lily has stayed at home since she left school. 要求：主句的谓v.用现在完成时，而且须是延续性动词；从句的谓v.用一般过去时，而且须是终止性动词。

总之，since用作介词的简单句，时态为现在完成时；since用作连词，引导时间状语从句，从句用一般过去时，而主句用现在完成时。