How may be the leech used in ayurvedic system of treatment??​

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."

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.