在虚拟语气中，何种情况下recommmend 的宾语从句中一定要省略should?

I recommend you to xxxxx

she should recommend this-
I should have recommended

use these two to say something that you must do...eg

recommend 当"劝告;建议"讲时,后面引导的宾语从句要虚拟,should + do should 可以省略,不一定非得省略