Question

part a
the four most common elements in living organisms are
o c, h, o, n
o c, h, o, na
o c, n, o, na
o c, h, o, fe

Explanation:

Carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) are the most abundant elements in living organisms. They are key components of organic molecules like carbohydrates, proteins, lipids, and nucleic - acids.

Answer:

C, H, O, N