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, answer the question "what is required for cell growth?" with the following options: 
- microscope
 - nitrogen
 - protein
 - carbohydrates
 - fat
 - nucleus
 - energy
 - Enzymes


 

   protein      