State and explain three main criteria used by scientist to classify organisminto different taxa ?

answer; ///(b) it is composed of four protein chains and four heme groups;

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.