应该选D what
Has it ever struck you 是主干,其中的it做形式主语,真正的主语是后面的 what主语从句即：
_what_ it would be like to have no one you could trust
what主语从句中what作介词like的宾语,it 是形式主语,真正的主语是后面不定式的to have no one you could trust.
you could trust又是一个定语从句修饰no one
翻译：没有你可信赖的人会是什么样子,这件事曾经触动你吗?