Assertion A : To estimate the rainfall over a catchment, the number of raingauges required per unit area is large for hilly areas.
Reason R : Rainfall gradient is steep.
Select your correct answer according to the coding system 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

Answer: Option A