According to the sources, humans have 12 pairs of ribs. The first seven pairs are true ribs, the 8th, 9th, and 10th pairs are false (vertebrochondral) ribs, and the last 2 pairs (11th and 12th) are not connected ventrally, and are thus called floating ribs. Therefore, the total number of floating ribs is 4 . Other options are incorrect because: (1) there are 20 types of amino acids that occur in proteins ; (2) there are 7 cervical vertebrae in humans ; and (3) the sources primarily distinguish between two major types of diabetes: Diabetes Insipidus and Diabetes Mellitus .