The correct answer is A.
Pushing the body harder than it's ready to be pushed during exercise can result in damage to the body. You should never overexert yourself during exercising, if you do you are putting extra pressure on your organs, on your muscles, on your tendons and ligaments and your bones. You should always exercise at the right level for your body and if you feel pain or dizziness then you either stop, slow down or change the exercise.