Boolean and audio is not working right

(the first part is to help you guys understand my script more better the question is near the bottom)ok i have a script that chooses one music out of 3 music (song 1 - song 3) for th background music which works good and when the player picks up the rocket power up the background music changes to the power up music or song 4 which works great to but when the power up effects is gone the song 4 is suppose to stop and the song that was playing before should continue playing but it doesn’t work and i don’t know how to make the other song continue playing do i need another audio source or something plz help

var song2 : AudioClip; 
var song3 : AudioClip;
var song4 : AudioClip;
var kill : boolean = true; 
var count : float = 0;


function Start () {


}

function Update () {  

if(choose){
var x = Random.Range(1,4); 
choose = (false); }


 
  if(x == 1) {
 audio.clip = song1;
 audio.Play();}
  
  
  if(x == 2){  
audio.clip = song2; 
audio.Play();} 
  
 if(x == 3){ 
audio.clip = song3; 
audio.Play();}

if(lifeanddeath.rocket == (true)){ 
audio.Pause();  
audio.clip = song4; 
audio.Play();} 


} 


}




	
 
 






function Awake () { 


		DontDestroyOnLoad (transform.gameObject); 

	
	
	}

Using multiple audio sources would probably be the easiest.
You could also check out audio.PlayOneShot for this purpose.