A PAM source generates four symbols 3 V, 1 V, -1 V and —3 V with probability of p(3) = 0.2, p(1) = 0.3, p(-1) = 0.3, p(—3) = 0.2 respectively. The variance for this source will be

A

4.2 V

B

3.2 V

C

3.6 V

D

4.6 V