How can I get the Interstitials to show

I am trying to show an interstitial ad in my game, but I can't figure out how to do it my script: using UnityEngine; using UnityEngine.Advertisements; using GoogleMobileAds.Api;

 public class ads : MonoBehaviour
 {
     static public bool showInterstitial = false;
     bool done = false;
     InterstitialAd ad;
 
     //Interstitial ad
 
 
     void Start(){
         RequestBanner();
         showInterstitial = true;
         RequestInterstitial();
 
     }
 
 
 
         private void RequestBanner()
     {
         #if UNITY_ANDROID
         string adUnitId = "ca-app-pub-2298967481644009/6636810571";
         #elif UNITY_IPHONE
         string adUnitId = "ca-app-pub-2298967481644009/6636810571";
         #else
         string adUnitId = "unexpected_platform";
         #endif
         
         // Create a 320x50 banner at the top of the screen.
         BannerView bannerView = new BannerView(adUnitId, AdSize.Banner, AdPosition.Bottom);
         // Create an empty ad request.
         AdRequest request = new AdRequest.Builder().Build();
         // Load the banner with the request.
         bannerView.LoadAd(request);
 
 
     }
 
 
     void RequestInterstitial()
     {
 
             #if UNITY_ANDROID
             string adUnitId = "ca-app-pub-2298967481644009/6636810571";
             #elif UNITY_IPHONE
             string adUnitId = "INSERT_IOS_INTERSTITIAL_AD_UNIT_ID_HERE";
             #else
             string adUnitId = "unexpected_platform";
             #endif
         
             // Initialize an InterstitialAd.
             InterstitialAd interstitial = new InterstitialAd (adUnitId);
             ad = interstitial;
             // Create an empty ad request.
             AdRequest request = new AdRequest.Builder ().Build ();
             // Load the interstitial with the request.
             interstitial.LoadAd (request);
             Debug.Log("done");
 
             // Called when an ad request has successfully loaded.
             interstitial.AdLoaded += HandleAdLoaded;
 
     }
 
     public void HandleAdLoaded(object sender, EventArgs args)
     {
         print("HandleAdLoaded event received.");
         Interstitial.show ();
         // Handle the ad loaded event.
     }    

I get this error: error CS0246: The type or namespace name `EventArgs' could not be found. Are you missing a using directive or an assembly reference?

I have watched some tutorials and examples, but I can't spot what I am doing wrong. the interstitial variable isn't global, so I can't use it outside the function. I have tried, but if you know what I might be doing wrong, please show me :)

I have tried to use the ad variable I declared, but when I am trying ad.Show(), I get an error.