CPR, or cardiopulmonary resuscitation, is a first-aid technique to help save lives. It involves compressions of the patient’s chest cavity. Which description is the best description of the functions of chest compressions in CPR?

answer choices :
Chest compressions are done to pump the heart.
Chest compressions are done to strengthen the rib bones.
Chest compressions increase carbon dioxide inhalation.
Chest compressions allow the patient's muscles to wake up.