Final answer:
To find the largest of four int variables using a max function, call the function three times within a single expression: max(max(population1, population2), max(population3, population4)). This uses the max function to compare pairs first, then the larger results.
Step-by-step explanation:
The question asks for an expression to find the largest value among four integer variables by using a max function that accepts two integer parameters and returns the larger of the two. To achieve this, you must call the max function three times. In the first two calls, you compare pairs of variables, then you compare the larger values from those two calls with the remaining variable to find the overall largest value. The expression would look like this:
max(max(population1, population2), max(population3, population4))
This expression first finds the larger of population1 and population2, then finds the larger of population3 and population4, and finally compares the two results to return the largest value among all four variables.