At one time we had about eighty people here who did nothing but ( ) into his family history.
A.Researched
B.To research
C.Researching
D.Research
正确答案是D
At one time we had about eighty people here who did nothing but ( ) into his family history.
A.Researched
B.To research
C.Researching
D.Research
正确答案是D