Question

-I ________ there are some books in the bag.

-No, I think there's a ball in it.

1. A.
   find
2. B.
   know
3. C.
   guess
4. D.
   see

Answer 1

C
根据上下文，可知对话双方都在判断包中是什么，如第一个人已确定，第二个人就不会说I think了，故填guess一词。