一道基本的英语语法题

问题描述:

一道基本的英语语法题
When he was here last year,our new library ________ .
A.was building
B.has been built
C.was being built
D.was to built
请问其他几个选项为什么是错的?

因为从句是过去时态,一般情况下,主句肯定也是过去的某种时态,再加上library是被建立的,所以选择过去进行时的被动语态 was/were +being+P.P.