This is the present perfect, which is constructed using: 例句：there happened to be a telephone booth. What happened?和what's happening?的区别是什么？ what happen?表示发生了什么，用于询问发生了什么事情，通常用于过去的事件或突发情况。
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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. The past participle of the main verb the. The helping verb have 2.
There happened to be是由there be句型演变过来的，仍是there be结构； it happened to be.，意思是：结果碰巧是.
'happend' is a spelling mistake of happened. 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. 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构成的过去.
When describing an event in the past speech, should i use present or past tense for happen.
