A set of 20 cards includes 12 red cards and 8 black cards. The cards are shuffled thoroughly and you pick one at random, observe its color, and replace it in the set. The cards are thoroughly reshuffled, and you again select a card at random, observe its color, and replace it in the set. This is done total of six times. Let X be the number of red cards observed in these six trials. The variance of X is
A. 6.
B. 3.60.
C. 2.4.
D. 1.44.