Which One of These 'X' Variables Is a Discrete Random

Multiple Choice

Which one of these 'X' variables is a discrete random variable?

A) An experiment in chemistry is repeated many times and X is the time required for a reaction to occur in seconds.
B) A student is randomly selected and X is the number of correct answers on a two question multiple-choice quiz.
C) A UPS package is randomly selected and X is the weight in pounds of the package.
D) A student is randomly selected and X is the distance they must travel in feet to go from their dorm room door to the door of their first class on Monday morning.