一言辨异 知道/看见

I have known him for ten years. But I didn’t recognize him just now because he has changed so much.

我认识他十年了。但他变化如此大，我刚才没有认出来。

——recognize是“认出”以前know(认识)的人或物。

They looked sadly at the master,because the master himself looked sad.

他们难过地看着老师，因为老师自个儿也显得悲伤。

——“look sadly at”意为“悲哀地，难过地看着”，look是实义动词，表示“看”;“look sad”意为“看起来悲哀、悲伤”，look是系动词，sad是形容词，作表语。