Which of the following is an example of a discrete variable?

A discrete variable is one that takes on a countable number of distinct values. In the context of the question, the number of stops a truck makes fits this definition perfectly. It can be enumerated as whole numbers; you can have 1, 2, 3 stops, and so forth, but not fractional stops. This characteristic clearly identifies it as a discrete variable.

In contrast, other examples provided, such as distance traveled, time taken, and weight of cargo, are all continuous variables. These can take on any value within a range and can be measured with greater precision leading to fractional values. For instance, distance can be measured in specific units such as miles or kilometers, and can easily include decimals, such as 5.7 miles. Similarly, time can be recorded in hours, minutes, and seconds, and weight can be tallied in pounds or kilograms, often resulting in decimal numbers. Thus, the only option that embodies a discrete nature is the number of stops a truck makes.