sad作形容词意思是“难过的、悲哀的”，在句中可用作定语，也可用作表语。用作表语时，其后可接介词短语、动词不定式或由that引导的从句。用作sad to say短语时意为“不幸的是”,常放在句首。
1.悲哀的；难过的；显得悲哀的
如：We are very sad to hear that you are leaving.
听说你要走了，我们十分难过。
2.令人悲哀的；让人难过的
如：It was sad to see them go.
看着他们离去，真让人难过。
3.让人无法接受的；该受责备（或批评）的
如：It's a sad fact that many of those killed were children.
让人难以接受的是遇难者中很多是孩子。
4.乏味的；过时的
如：You'd have to be sad to wear a shirt like that.
你穿着那样的衬衣显得老气。
5.状况不佳的
如：The salad consisted of a few leaves of sad-looking lettuce.
色拉就是几片生菜的残叶。
6.可惜的是；很遗憾
如：Sad to say, there are not very many of them around.
很遗憾，这种医院并不多。
