What _______ (happen ) over there?Let's go and see.

What _______ (happen ) over there?Let's go and see.
What _______ (happen ) over there?Let's go and see.

What _______ (happen ) over there?Let's go and see.
happened
应该填过去式,因为happen不能用于进行时态,是短暂性动词.
希望能帮到你,祝更上一层楼O(∩_∩)O
有不会的欢迎再继续问我(*^__^*)

is happening 正在发生什么 Let's go and see 由此看出是正在发生

happened, 那边发生了什么，让我们去看看，事情一定发生了，所以用过去式.

happened