Given below are two statements,one is Assertion $(A)$ and the other is Reason $(R).$
Assertion $(A):$ Natural rubber is a linear polymer of isoprene called cis-polyisoprene with elastic properties.
Reason $(R):$ The cis-polyisoprene molecules consist of various chains held together by strong polar interactions with a coiled structure.
In the light of the above statements,choose the correct one from the options given below:

• 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 true.