Question

【题目】The most difficult thing _____ they have to finish their work in 3 hours.

A. to B. is to C. that D. is that

Answer 1

【答案】D

【解析】

句意：最困难的事情是他们必须在三个小时内完成工作。to到…是一个介词或者是动词不定式的符号；is to是系动词后面跟to短语；that连词，引导从句；is that是系动词is后跟that引导的表语从句。根据句子结构可知，这句话是一个主系表结构，主语是The most difficult thing；is是系动词，后面跟that引导的表语从句。故应选D。