It was sad to see them go.
看着他们离去，真让人难过。
You'd have to be sad to wear a shirt like that.
你穿着那样的衬衣显得老气。
I was very sad indeed to hear of your father's death.
听到令尊大人去世，我感到非常难过。
We are very sad to hear that you are leaving.
听说你要走了，我们十分难过。
Her moods kept changing ─ now happy, now sad.
她的情绪总是变幻不定——时而欢喜，时而忧伤。