The correct option is B Both A and R are true but R is not a correct explanation of A
The heart’s four chambers are:
a) Right atrium: This chamber receives oxygen-depleted blood returning from the body and pumps it into the right ventricle.
b) Right ventricle: The right ventricle pumps blood from the right atrium to the pulmonary artery that sends the deoxygenated blood to the lungs, where it picks up oxygen.
c) Left atrium: This chamber receives oxygenated blood from the lungs and pumps it to the left ventricle.
d) Left ventricle: The thickest of all the chambers, the left ventricle is the difficult working part of the heart as it pumps blood throughout the whole body.
Therefore A and R are true, but R is not a correct explanation for A.