-----will your father be back from work?-----In half an hour.A. How longB. How soonC. when

问题补充：

-----will your father be back from work?

-----In half an hour.

A. How long

B. How soon

C. when

D. How often

答案：

A. How long

(答案→)B. How soon

C. when

D. How often

解析：How long多长;How soon多久;when什么时候;How often多久一次.根据下文,半个小时后,可知上文提问的是多久,故选B.