What do all four of these molecules have in common?

A.

They are essential to life.

B.

They carry signals.

C.

They are water soluble.

D.

They act as a source of energy

A. They are Essential to Life

I did a quick search and found the diagram. Let's go through these and solve by elimination.

B. Proteins can act as receptors which I guess could be considered a signal, but the rest of the molecules do not. B is incorrect.

C. Lipids are not water soluble. An example of lipids are fats, and oils. Have you ever tried combining water and oil? Think about salad dressing, it does not mix. C is incorrect.

D. Carbohydrates and lipids are sources of energy, but nucleic acids and proteins are not. D is incorrect.

The answer is A. because we know that our bodies are made up of nucleic acids, protein, fats, and we need carbohydrates in order to live normal, healthy lives.