the reason it is for sure that yawning can be passed from person to person.A. WhateverB.

问题补充：

the reason, it is for sure that yawning can be passed from person to person.

A. Whatever

B. Wherever

C. Whichever

D. However

答案：

(答案→)A. Whatever

B. Wherever

C. Whichever

D. However

解析：考察从句连词选择。Whatever无论什么 ，用语名词前，wherever无论何地，作地点状语 whichever无论哪一个，用于有范围的时候 however无论多么，用语形容词前

句意为，无论是什么原因，可以肯定的是打哈欠是可以从一个人传染到另一个人的。