Given below are two statements: One is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$: The stretching of a spring is determined by the shear modulus of the material of the spring.
Reason $(R)$: $A$ coil spring of copper has more tensile strength than a steel spring of same dimensions.
In the light of the above statements,choose the most appropriate answer from the options given below:

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