For the following numerical variables, state whether each is discrete or continuous.
a. The length of a 1-year-old rattlesnake
b. The altitude of a location in California selected randomly by throwing a dart at a map of the state
c. The distance from the left edge at which a 12-inch plastic ruler snaps when bent sufficiently to break d. The price per gallon paid by the next customer to buy gas at a particular station.