As a rule you can borrow only two books in the library.A. at one timeB. at a timeC. in n

问题补充：

As a rule, you can borrow only two books in the library.

A. at one time

B. at a time

C. in no time

D. at times

答案：

A. at one time

(答案→)B. at a time

C. in no time

D. at times

解析：“作为一个规定，一次你只能从图书馆借一本书。”at one time“曾经”，at a time”一次”，in no time“立刻”，at times“有时候”，所以答案B。