Everyone in our class was working hard and doing what we could a good college.A. enter。mB

问题补充：

Everyone in our class was working hard and doing what we could a good college.

A. enter。m

B. to enter

C. entering。m

D. entered

答案：

A. enter。m

(答案→)B. to enter

C. entering。m

D. entered

解析：此句为省略句，即在 could 后省略了动词 do，若把句子补完整应为Everyone in our class was working hard and doing what we could do to enter a good college。即句中的不定式短语(to enter a good college)是用作目的状语的，而不是与情态动词(could)一起构成谓语。