— You speak French so well. How long have you learned it?— I was fifteen.A. UntilB. Since

问题补充：

— You speak French so well. How long have you learned it?

— I was fifteen.

A. Until

B. Since

C. When

D. Before

答案：

A. Until

(答案→)B. Since

C. When

D. Before

解析：since +一般过去时，相当于用延续性动词，how long应该与延续性动词连用，故选答案为B