Determine whether X is a binomial random variable.

a. A fair die is rolled 20 times. Let X be the number of times the die comes up 6.

b. A standard deck of 52 cards contains four aces. Four cards are dealt without replacement from this deck. Let X be the number that are aces.

c. A simple random sample of 50 voters is drawn from the residents in a large city.

Let X be the number who plan to vote for a proposition to increase spending on public schools.