﹣Why are the windows so dirty?﹣Because we __________ them for a long time.A. have cleaned B. haven’t cleaned C. didn’t clean
The classroom is very _______ because some students are making some _______.
-Do the interesting books belong to________? - No, they are the __________ .
We had fun________ in the swimming pool last Sunday.
There must be a boy ________ basketball outside the door. I hear him crying.
Have you done ____ to improve the environment ?