Which Line in the Following Program Contains the Header for the ShowDub

Which line in the following program contains the header for the showDub function?
1 #include <iostream>
2 using namespace std;
3 void showDub(int) ;
4 int main()
5 {
6 $\quad$ int x = 2;
7 $\quad$ showDub(x) ;
8 $\quad$ cout << x << endl;
9 $\quad$ return 0;
10 }
11 void showDub(int num)
12 {
13 $\quad$ cout << (num * 2) << endl;
14 }

A) line 3
B) line 4
C) line 7
D) line 11