Stop Specific Audio on a Script with multiple Sounds?

Hi, I have 2 sounds on a script a fire sound and a thruster sound. How to I stop 1 specifically on 1 script because right now if I move forward, my thruster sound goes and loops and is fine, but when I shoot while moving forward then my fire sound goes and loops and the thruster stops. I just want to have the thruster loop while I hit W and the fire not loop but play once when I shoot, they are both in the same script and same game object. Here is my code.

 using UnityEngine;
 using System.Collections;
 
 public class Shooting_CJ : MonoBehaviour {
     public AudioClip Laser;
     public AudioClip Thruster;
 
     // Use this for initialization
     void Start () {
         
         
     }
     
     // Update is called once per frame
     void Update () {
         if (Input.GetKeyDown("space"))
         {
             audio.clip = Laser;
             audio.Play();
         }
 
         if (Input.GetKeyDown(KeyCode.W))
         {
             audio.loop = true;
             audio.clip = Thruster;
             audio.Play();
         }
         if (Input.GetKeyUp(KeyCode.W))
         {
             audio.Pause();
             audio.loop = false;
         }
         else
         {
             
             
         }
     
     }
 }