GATE EXAM PREPARATION IN "C" - C function (GATE CS 2004)

Consider the following C function

void swap (int a, int b) {    int temp;    temp = a;    a = b;    b = temp; }

In order to exchange the values of two variables x and y. 

a) call swap (x, y)
b) call swap (&x, &y)
c) swap (x,y) cannot be used as it does not return any value
d) swap (x,y) cannot be used as the parameters are passed by value

Answer(d)
Why a, b and c are incorrect?
a) call swap (x, y) will not cause any effect on x and y as parameters are passed by value.
b) call swap (&x, &y) will no work as function swap() expects values not addresses (or pointers).
c) swap (x, y) cannot be used but reason given is not correct.