Which of the Following Describes the Atomic Makeup of the Backbone

Which of the following describes the atomic makeup of the backbone unit of a protein?

A) 2 carbon atoms, 2 nitrogen atoms, 2 oxygen atoms
B) 3 carbon atoms, 2 nitrogen atoms, 2 oxygen atoms, 1 hydrogen atom
C) 3 carbon atoms, 1 nitrogen atom, 1 oxygen atom, 1 hydrogen atom
D) 3 carbon atoms, 2 nitrogen atoms, 2 oxygen atoms, 2 hydrogen atoms