----- As we know, you won’t go back to the USA since you have established a research center here．But how long in America?
----- For almost 10 years．
A. did you study
B. have you studied
C. were you studying
D. have you been studying
网友回答
(答案→)A. did you study
B. have you studied
C. were you studying
D. have you been studying
解析：可联系答.案.网客服索取。