I was reading a grammar book where the author said " what happened? " as a complete meaningful sentence. I am not clear how can it be a complete sentence? Can someone explain me the logic behind it? I consider a complete meaningful sentence as a sentence which has both subject and verb. In this sentence which is subject and which is verb. Please help me in getting this understood. Thanks in advance.
What is the subject, happened is the verb. It's an interrogative sentence. In order to understand the role of the interrogative word in a question, answer it. Example:
What happened? An explosion happened.
An explosion is the subject, therefore what was also the subject.
What are you thinking? I am thinking bananas.
Bananas is the object, therefore what was the object.