"A family has two children. Suppose that the birth of each child is an independent event and that it is equally likely to be a boy or a girl. Let C denote
the event that the family has one boy and one girl. Let D denote the event that the family has at most one girl. Which of the following must be true about events C and D?
a. C and D are independent events.
b. C occurs given that D does not occur.
c. C and D are not independent events.
d. C and D are mutually exclusive events."