Answer:
The correct answer is B.
Explanation:
I feel like the most effective choice is C.
The answer is one mystery that still remains unsolved is why we yawn.
and another theory is that when you yawn it sends oxygen to the brain causing your body to be able to stay awake, hence when you are tired and need to stay awake you yawn a lot.
A is the answer jsjsjsjsjwijsiw
It provides background information on the topic.
and It gives the main topic of the paper.
