问题补充:
One of the most important questions they had to consider was of public health.
A. what
B. this
C. which
D. that
答案:
A. what
B. this
C. which
(答案→)D. that
解析:考察代词。本句中的系动词was后面不是一个完整的句子,所以不能使用AC项。That指代前面的名词problem,后面有定语修饰,表示特指。句意:他们不得不快乐的问题之一就是公共健康的问题。故D正确。