Question to you: What is something cells cannot survive without?
Options:
- (A) gas
- (B) Air
- (C) O2
- (D) CO2
- (E) Ca
- (F) O3
- (G) Fe
- (H) He.
Let's reason step-by-step:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Cells cannot survive without oxygen. And oxygen, O2, is the molecule to do it. Cells cannot survive without O2. Final answer: (C).