Sound by clicking fire1 button

hello, i’ve got a problem because i was folowing a tutorial in youtube to play a sound every time i click the mouse button but i get “BCE0023: No appropriate version of ‘UnityEngine.AudioSource.PlayOneShot’ for the argument list ‘(String)’ was found.”
here is the script

var RevolverSoundEffect : AudioClip ;
function Start () {

}

function Update () {
 if (Input.GetButtonDown("Fire1"))
 {
   audio.PlayOneShot(Revolver Sound Effect);
   }
}

audio.PlayOneShot(Revolver Sound Effect);

Should be

audio.PlayOneShot("Revolver Sound Effect");

When you’re calling a user-defined setting, you have to wrap it in quotes.