The correct answer is: "An expression is evaluated."
Explanation:
Inside the parentheses of a while loop, there is a conditional statement (or expression) that is evaluated. For example:
int a = 10;
while(a>0) {
cout << a << endl;
a--;
}
In the above snippet of code, you can see that inside the parentheses of a while loop, there is a condition (or expression) a > 0. It is evaluated in every iteration. If that condition meets (or true), the block of while loop will be executed. Hence, the correct answer is "an expression is evaluated."