问题补充:
-- will you come back from the library, Linda?
-- In an hour.
A. What time
B. How often
C. How soon
D. How long
答案:
A. What time
B. How often
(答案→)C. How soon
D. How long
解析:What time什么时间;How often多久一次;How soon多久;How long多长。根据答语,一小时后,可知问的是时间长久,故选C。