Assertion $(A)$: In the daytime, $CO_2$ generated during respiration is used up for photosynthesis.
Reason $(R)$: There is no $CO_2$ release during the day.

• A
  Both $(A)$ and $(R)$ are true and $(R)$ is the correct explanation of $(A)$.
• B
  Both $(A)$ and $(R)$ are true, but $(R)$ is not the correct explanation of $(A)$.
• C
  $(A)$ is true, but $(R)$ is false.
• D
  $(A)$ is false, but $(R)$ is false.