Mother insisted that__ .

问题描述:

Mother insisted that__ .
A they are to be back before nine in the evening.
B they ought to be back before nine in the evening.
C they be back before nine in the evening.
D they had to be back before nine in the evening.

选C
意思是“坚持要”,表示命令、要求,其后之宾语从句要用虚拟式动词原形
或者“should + 动词原形”
此处为表示命令
意思是“坚持说”,后面从句该是什么时态就是什么时态,不用虚拟~