—Why are your shoes so dirty?-Because I ( ) the classroom.

问题描述:

—Why are your shoes so dirty?-Because I ( ) the classroom.
A.cleaned B.have cleaned C have been D.was cleaning

A
因为“我打扫了教室”应该用一般过去式,而且“Why are your shoes so dirty?”是一般现在时,时态要对应