For each variable, determine whether it is best thought of as discrete or continuous.

Variable Discrete Continuous

(a) The number of tickets purchased by a caller on a Rose Bowl ticket hotline

(b) The mass of the solid impurities per milliliter of Los Angeles tap water

(c) The amount of coffee in a cup dispensed by a coin-operated coffee machine

(d) The number of cellular phones owned by a family of four in Boston