sad是形容词。
难过的;悲哀的,令人悲痛的;凄惨的,阴郁的(形容颜色)的意思。如:
①She looked sad and tired.她看上去伤心且疲惫。
②I have a sad news for you.我有个令人遗憾的消息告诉你。
③We were all sad at her going.我们对她的离去都很难过。
④We are very sad to hear that you are leaving.听说你要走了,我们十分难过。
⑤Separation from his friends made him sad .与朋友们分离使他伤心。