Assertion A.: A free board of 0.3 m is provided above the top sewage line in septic tanks. Reason (R): It helps to accommodate the scum in the septic tank_________________?

A. Both A and R is true and R is the correct explanation of A
B. Both A and R is true but R is not a correct explanation of A
C. A is true but R is false
D. A is false but R is true