Assertion (A): To have maximum hydraulic efficiency, the trapezoidal section of an open channel should be a half- hexagon.
Reason (R): For any cross- section, a hexagon has the least perimeter.
(a) Both A and R are individually true and R is the correct explanation of A.
(b) Both A and R are individually 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