TASK DEFINITION: Given a scientific question and its correct answer, generate supporting facts for the answer. This supporting fact can be an explanation for the answer to the given question.
PROBLEM: Question: What is the most common cause of lung cancer? Answer: tobacco smoke exposure

SOLUTION: The new cells gradually move up through the epidermis toward the surface of the body. As they move, they produce the tough, fibrous protein called keratin.

PROBLEM: Question: How do reptiles typically reproduce? Answer: sexually

SOLUTION: Reptiles typically reproduce sexually and lay eggs.

PROBLEM: Question: Density is defined as the mass of an object divided by its what? Answer: volume

SOLUTION:
Density is defined as the mass of an object divided by its volume. Propose a unit of density in terms of the fundamental SI units.