问题

We ____ on this project for four hoursLet’s have a rest

A:are working
B:have been working
C:worked
D:had worked

正确答案是：

同类题型

The scientist corresponds with colleagues in order tolearn about matters ______ to her own research

Teachers should create an environment children are taught how to solve problems of learning by themselves.

Nice to meet you, Mike. ________ —Everything is OK. Thanks.

The students were made ______ the text tentimes.