Which of the following situations would provide a random sample that is not biased?

a) Determining the average number of hours
per week that people exercise, by
randomly surveying 200 members of
"Muscle Beach Gym".
b) Determining who will win the election for
Senior class president, by randomly
surveying 100 seniors after they vote.
c) Determining the average number of dogs
per household in a city, by randomly
surveying 100 people attending a pet
show in the city.
d) Determining the perceħt of households
who have at least 1 computer, by
randomly surveying 500 customers at a
computer store