Assertion (A): The frequency of floods in North Indian plains has increased during the last couple of decades. Reason (R): There has been reduction in the depth of river valleys due to deposition of silt.

1. (a)Both A and R are true, and R is the correct explanation of A
2. (b)Both A and R are true, but R is not a correct explanation of A
3. (c)A is true, but R is false
4. (d)A is false, but R is true