-How long do you think it is he arrived here?-No more than half a year I believe.

问题补充：

---- How long do you think it is he arrived here?

---- No more than half a year, I believe.

A. when

B. that

C. before

D. since

答案：

A. when

B. that

C. before

(答案→)D. since

解析：考查固定短语。句意：自他到这儿以来，你认为多久啊？故用since。