What value is passed to the first parameter?

source file: mySource.js:
```
1. function product(x.y);
2. {
3. var x; var y; var product;
4. product = x * y;
5. return (product);
6. }
```
web page script, assume the file links to mySource.js:
```
1. function math();
2. {
3. var num1 = 3; var num2 = 4;
4. var result = product(num2, num1);
5. document.write(num2 + " X " + num1 + " = " + result);
6. }
7. function product(a.b);
8. {
9. var a; var b; var answer;
10. answer = a * b * b;
11. }
```

a. 4
b. 3
c. a
d. x

a. 4