A complete protein:

a. has not been denatured.

b. contains all 20 amino acids.

c. contains all 9 essential amino acids.

d. is composed of only di - and tripeptides.

c. contains all 9 essential amino acids.

A complete protein contains all 9 essential amino acids. A protein is a macromolecule that is made of amino acids. There are 20 amino acids that our body needs in order to survive, but out of these 20, only 9 are not produced in some form by the body, so we have to acquire them through food. A complete protein is a protein that contain all of those 9 essential amino acids that we don't produce.