optional variables in public static void

Hi !
Let's say I have the following;
public static void TryOut(int intOne, int intTwo, string strone, string strtwo)

{

....

}

And after I created dll, I will use it like that;
TryOut(1,3,"bla bla bla", "bla bla bla");
But I want the last variable to be optional. I mean this method could be used like that;
TryOut(1,3,"bla bla bla", "bla bla bla");
And Also like that
TryOut(1,3,"bla bla bla");
 
I know it is possibel but how I could do that I have no idea ! Pls help !
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