Final answer:
The correct answer is option B: the variable x (or its memory location). When the function is called with x as the first argument, since the parameter int& value1 is a reference to int, the function f1 receives a reference to the variable x.
Step-by-step explanation:
The function 'f1' receives a reference to the variable 'x' (option B) as its first parameter, which allows the function to modify 'x' directly. This means that the function can modify the variable x directly, and any changes made to value1 within the function will affect the variable x outside the function. In contrast, int value2 is a value parameter, so the function f1 receives a copy of the value of y, which does not allow the function to alter the variable y outside of its scope.
In the given function declaration, the first parameter is declared as int& value1, which means it is a reference to an integer. When the function is called with f1(x, y), it passes the variable x (or its memory location) as the argument for the first parameter.
This means that any changes made to the parameter value1 inside the function will affect the original variable x in the calling code.