Question

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

---______ I was fifteen.

1. A.
   Until
2. B.
   Since
3. C.
   When
4. D.
   Before

Answer 1

B
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