Which one of the following items gives its correct total number?

Humans have 12 pairs of ribs.
The first seven pairs are true ribs (attached directly to the sternum), and the 8th, 9th and 10th pairs are false or vertebrochondral ribs (attached to the seventh rib through hyaline cartilage).
The last 2 pairs (11th and 12th) are not connected ventrally and are called floating ribs. Two pairs means 4 floating ribs in total, so this item is correct.
The number of cervical vertebrae in humans, as in almost all mammals, is 7, not 8.
The number of amino acids found in proteins is 20, not 16.
Diabetes is generally of two types: diabetes mellitus and diabetes insipidus.
So the item with the correct total number is floating ribs in humans - 4.