They——to enter the building by the back door; howerve,the front door was locked.

问题描述:

They——to enter the building by the back door; howerve,the front door was locked.
A.weren't supposed B.wouldn't be supposed C.were supposed D.would be supposed 为什么呢?为什么D错误?

先根据情景翻译:尽管前门是关着的,他们还是不打算从后门进入大楼.
be supposed to 打算做.,此为虚拟语气用法,所以用were