—will your sister be back ?—In about two hours.A. HowB. How often C. How longD. How soon

问题补充：

—will your sister be back ?

—In about two hours.

A. How

B. How often

C. How long

D. How soon

答案：

A. How

B. How often

C. How long

(答案→)D. How soon

解析：How怎样；How often多久一次；How long多长；How soon多久。根据下文，在大约两个小时后。可知上文问的是多久，故选D。