Q: Fact 1: Protein is used to repair cells by the human body. Fact 2: Protein is necessary for growth and repair. Given the two facts above, what is required for cell growth?

Available options:
(A). microscope;
(B). nitrogen;
(C). protein;
(D). carbohydrates;
(E). fat;
(F). nucleus;
(G). energy;
(H). Enzymes;
The answer is:
(C).