Ethylene has is not _. A . A plant hormone that affects ripening. B. Used by growers to cause stems to lengthen .c. A stimulus . D. A cause of leaves falling down from a plant

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.