Question

it is necessary that she_once a week to help me with my lessons.A came B would come C come D comes

Answer 1

答案选B would come
这里是虚拟语气，It is necessary that sb should do sth 走某事是很必要的。虚拟语气的结构是should / would /could do sth.

虚拟语气中的should不是可以省略吗?
不是所有的虚拟语气should都可以省略的，上面那种句型的就不可以省略。 当由suggest 引导的宾语从句的虚拟语气才可以省略
例如 I suggest that you (should) get up earlier.

Answer 2

c 在it is necessary + that ……的结构中，that 引导的主语从句的谓语动词要用虚拟语气，即should+动词原形，其中的should是可以省略的

Answer 3

D