Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R).$
Assertion $(A):$ Photochemical smog causes cracking of rubber.
Reason $(R):$ Presence of ozone,nitric oxide,acrolein,formaldehyde and peroxyacetyl nitrate in photochemical smog makes it oxidizing.
Choose the most appropriate answer from the options given below:

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