________ others say, the professor is sure that his theory is correct．

A.No matter

B.It doesn't matter

C.Whatever

D.What

答案及解析： C

解析：

whatever＝no matter what无论什么，whenever＝no matter when无论什么时候；however＝no matter how无论怎样，它们都可引导让步状语从句。如：Whatever(＝No matter what)you do, don't keep him waiting！无论你做什么，都不要让他久等！