we were curious to find out what had happed.这里的what是是用法,为什么这样用

we were curious to find out what had happed.这里的what是是用法,为什么这样用
we were curious to find out what had happed.这里的what是是用法,为什么这样用

we were curious to find out what had happed.这里的what是是用法,为什么这样用
这是代词what的一种特殊用法.即这里的what=the things that,what在宾语从句中做主语.
we were curious to find out what had happed=we were curious to find out the things that had happed.

what happens 主语+ 谓语 ：发生了什么事， 事情作主语，

上面句子是过去完成时：what had happened

该句是宾语从句句式。即what had happed 作find out的宾语。what 又做从句中的主语。