title: the import android could not be resolved
body: <p>I opened a project that I had not opened in a while in Eclipse today. I was unable to compile due to some (inexplicable) errors.</p>
  
  <pre><code>import android.app.Activity;
  import android.os.Bundle;
  import android.view.animation.AnimationUtils;
  import android.widget.ImageView;
  import android.view.animation.Animation;
  import android.content.Intent;
  </code></pre>
  
  <p>produces the following error:</p>
  
  <blockquote>
    <p>the import android could not be resolved</p>
  </blockquote>
  
  <p>What can I do to resolve this problem?</p>