Assertion (A): Large concave mirrors are used to concentrate sunlight to produce heat in solar cookers. Reason (R): Concave mirror converges the light rays falling on it to a point.

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.