What's the matter? You look sad.
你怎么了?显得这么伤心。
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今天的几个句子是有关担心、惦念的:1.What's going on? 到底怎么回事?2.What are you worried about? 你担心什么?3.You look grave. 你今天看上去很悲伤。4.You look sad today. 你今天怎么满脸的不高兴。