问题补充:
He tried his best to solve the problem, difficult it was.
A. whatever
B. however
C. whichever
D. wherever
答案:
A. whatever
(答案→)B. however
C. whichever
D. wherever
解析:No matter +特殊疑问词引导让步状语从句,意为:无论…;意为后面接形容词difficult,所以使用how.而不是what. 句意:无论问题有多难,他都全力以赴地解决它。故B正确。