问题补充：
— can I keep the books? —Two weeks.
A. How long
B. How often
C. How far
D. How soon
答案：
(答案→)A. How long
B. How often
C. How far
D. How soon
解析：句意：这些书我可以保存多久？两个星期。how long 就一段时间提问；how often就频率提问；how far 就距离提问；how soon 就“多快，多久”提问；根据后面的two weeks可知，是提问的时间之久，所以用how long；故选A。
