the import android could not be resolved
<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>
