One of the most important question they had to consider was ____of public health.

问题描述:

One of the most important question they had to consider was ____of public health.
A.what B.this C.that D.which
为啥this不行

C
that of public health是表语从句,this不可以做表语从句的引导词的.that of public health是表语从句,咋没有先行词呀?并不是所有的从句都要先行词的。这句话主语:One of the most important question they had to consider系动词:was表语(从句):that of public health