title: How to fix Type does not contain a definition for 'Show' and no extension method could be found
body: <p>Hello everyone how are you? I'm fine.
  I'm trying to write the scripts for a Unity3d game monetization.
  I've written the script to initialize the Admob ads and now I'm writting another script for Load and Show the ads. I'm following the Admob tutorial, but I have some errors that I don't know how to fix.</p>
  <blockquote>
  <p>The type 'InterstitialAd' does not contain a constructor that takes '1' arguments</p>
  <p>Type 'InterstitialAd' does not contain a definition for 'LoadAd' and no extension method 'LoadAd' of type 'InterstitialAd' could be found. Are you missing an assembly reference?</p>
  <p>Type 'InterstitialAd' does not contain a definition for 'IsLoaded' and no extension method 'IsLoaded' of type 'InterstitialAd' could be found. Are you missing an assembly reference?</p>
  <p>Type 'InterstitialAd' does not contain a definition for 'Show' and no extension method 'Show' of type 'InterstitialAd' could be found. Are you missing an assembly reference?</p>
  </blockquote>
  <p>It seems that I have to write a constructor, and the methods are not defined but I'm following the instructions of AdMob monetization guide, and It's supposed that using the Admob api will load the methods, but it doesn't work.</p>
  <p>This is my code:</p>
  <pre><code>    using System.Collections;
      using System.Collections.Generic;
      using UnityEngine;
      using GoogleMobileAds.Api;
  
      public class InterstitialAd : MonoBehaviour 
      {
          private InterstitialAd interstitial;
          private string adUnitId;
  
          private void requestInterstitial() 
          {
              //Los siguientes adUnitId son anuncios de prueba, antes de publicarlo debo reemplazar adUnitId con el id del bloque de anuncios
  #if UNITY_ANDROID
              string adUnitId = &quot;ca-app-pub-3940256099942544/1033173712&quot;;
  #elif UNITY_IPHONE
              string adUnitId = &quot;ca-app-pub-3940256099942544/4411468910&quot;;
  #else
              string adUnitId = &quot;unexpected_platform&quot;;
  #endif
  
              // Initialize an InterstitialAd. //Id Del bloque de anuncios
              this.interstitial = new InterstitialAd(adUnitId);
              // Use this for initialization
              // Create an empty ad request.
              AdRequest request = new AdRequest.Builder().Build();
              //Load the interstitial with the request interstitial
               this.interstitial.LoadAd(request);
          }
  
          //ShowAd
          private void showInterstitial() 
          {
              if (Time.time % 45 == 0 &amp;&amp; Time.timeSinceLevelLoad &gt; 60 &amp;&amp; this.interstitial.IsLoaded()) 
              {
                  this.interstitial.Show();
              }
          }
      }
  </code></pre>
  <p>I hope you can help me! It's the final step for publishing my app !</p>