Mark the letter A, B, C, or D to indicate the correct answer to each of the following questions.

Câu hỏi

I think_outside in the open air is much more enjoyable than_exercise in some stuffy gyms.

A. to walk - done

B. walking – doing

C. walk - to be doing

D. having walked - do

I think_______outside in the open air is much more enjoyable than_______exercise in some stuffy gyms.