Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : Relative thickness of the different limbs (the thin descending limb, thin ascending limb and thick ascending limb) of loop of Henle is different but lumen diameter is same.
Reason (R) : Difference in relative thickness is due to differences in the thickness of epithelial cells but does not refer to change in lumen diameter.
In light of the above statements, choose the most appropriate answer from the options given below.