The fact that fun is not equal to happiness may be the opposite of many people actually understand.
A. why
B. that
C. which
D. what
网友回答
A. why
B. that
C. which
(答案→)D. what
解析：考察宾语从句。What引导宾语从句what many people actually understand并作为understand的宾语。Which指特定范围内的某一个。故D正确。