问题补充：
—The problem isn difficult for the children to work out, is it？
— . Perhaps they should have been given a more difficult one.
A. Yes, it is
B. Yes, it isn
C. No, it is
D. No, it isn
答案：
A. Yes, it is
B. Yes, it isn
C. No, it is
(答案→)D. No, it isn
解析：从后句可知,“本应该给他们一道更难的题”暗示原来所给的题不难,故答案是“不难”,但由于问句用的是否定形式,所以应用No, it isn .
