简单理解：be upset 为系表结构，后面的介词短语表示“原因”。不必细分是被动还是系表了，这对英语学习意义不大。
be upset about sth 对某事感到心烦,不安. be upset with sb about sth 因某事对某人感到心烦. eg.He was upset at his uncle about laughing all the time. …
如果想表达 “生某人的气”，那么可以用搭配 “be angry with someone” 或者 “get angry with someone”， 还有 “be upset with someone” 或者 “get upset with …
be upset at sb 对某人感到心烦,不安. be upset about sth 对某事感到心烦,不安. eg.He was upset at his uncle about laughing all the time. 解析看不懂？.
其实upset并不是描述某一种特定的心情，而是描述一种平静被打乱的状态。upset也可以做动词，表示”打翻“搅乱“，就像一杯咖啡被猫撞翻了，就是The cat upset the …
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