---How long do you think it is he took up the job?Half a year at least.A. whenB. befor

问题补充：

---How long do you think it is he took up the job?

--- Half a year at least.

A. when

B. before

C. that

D. since

答案：

A. when

B. before

C. that

(答案→)D. since

解析：句型：it is+段时间+ since“自从他干这项工作多长时间了？”“至少半年了”