问题补充：
---What do you often do your free time ?
--- I often read. I read interesting books .
A. in; lot
B. on; a lot of
C. in; lots of
D. on; a lot
答案：
A. in; lot
B. on; a lot of
(答案→)C. in; lots of
D. on; a lot
解析：在某人的闲暇时间，用介词in，因此将答案BD排除，同时a lot of可以修饰名词，而lot不能，故选答案为C
