What's up?=What's the matter?=What happened? 发生了什么事? 当被提问到这个问题时, 你只需向提问者阐明发生什么事就行 没什么事就回答"Nothing happened"或者“Nothing”
第2个回答 2006-10-19
what's up [简明英汉词典] 怎么了, 发生什么啦
回答是no problem/it doesn't matter
我老师说象" 哇操"本回答被提问者和网友采纳
第3个回答 2006-10-19
It also can used in daily greeting which share the same meaning with "what's going on". You can answer "fine,just class/work/okay" or "nothing" as the upstairs have answered.