Please help It is making me cry

b is the best answer for this question.

answer; i believe the answer is hydraulic action;

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.

radon is correct hope this