"We played for hours" is a complete sentence.
Answer: B
Step-by-step explanation
It is a sentence because it has at least one subject clause and a predicate.
In the above sentence, the subject is we and the predicate is played.
A subject is anything in the sentences such as a person or object doing the action.
The predicate describes the subject's actions.
This is a basic sentence and the requirement is that it should have subject and predicate.
In addition, a complete sentence has a clear meaning that doesn't leave the reader having any lingering questions regarding the conveyed message.