This is the present perfect, which is constructed using: What happened还是what's happenedwhat happened和what's happened都用于询问过去发生了什么事情，主要的区别在于语法和使用方式。what happened是一个过去时态的简单 Here, what's is the contraction of what has.
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The helping verb have 2.
The past participle of the main verb the meaning is.
What happened 和 what's happened两者的区别： 是问 what happened？只是想知道过去所发生的事情， 而如果用what's happened？则强调对现在的影响。，即想知道过去所发生的什么事导致了说话时. Happened to /happened with 区别区别只有一点，就是指意不同：1、happen to sb“某人发生了某事”。可指坏事，也可指好事。例句：what's happened to her? 接下来让我们看下what happen和what happened的用法区别： 1.词性：what happen是用原形动词happen构成的现在时短语，而what happened是用动词happen的过去式happened构成的过. 'happend' is a spelling mistake of happened.
