Towards evening, the patient opened his mouth as if _____ something to his son.

as if to do sth.似乎要做什么。 选C.

哈哈他们都没翻译整句！！
我来：将近傍晚，那病人张开他的嘴，似乎要对他的儿子说什么。

这个是最直白的翻译。
美化：傍晚时分，病人的嘴动了动，似乎有事情要向儿子交待。

满意了吧～

to say 要说
as if to do sth好像要做某事

C