students are told _____very careful when they are doing experiment.

问题描述:

students are told _____very careful when they are doing experiment.
a.should be b.be c.to be d.will be
这该选什么,为什么,和什么语法有关,

C
tell sb to do sth 吩咐某人做某事【的被动式】
be told to do sth