Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Ascending limb of loop of Henle is impermeable to water and allows transport of electrolytes actively or passively. Reason (R) : Dilution of filtrate takes place due to efflux of electrolytes in the medullary fluid. In the light of the above statements, choose the correct answer from the options given below :

• A

  Both $(A)$ and $(R)$ are true and $(R)$ is the correct explanation of $(A)$
• Correct answer
  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 true but (R) is true

Hence, the correct answer is option: 'B'.