title: LINQ select List where sub-list contains item from another list
body: <p>I can't wrap my head around how to create this query. I need to select the items in List 1, if the items Cats list contains a Cat object matching the ID of one of the Cats in List2. Is this possible? Thank you</p>
  
  <pre><code>List1&lt;pet&gt; List1 = new List&lt;pet&gt;(100);
  List2&lt;cat&gt; List2 = new List&lt;cat&gt;(30);
  
  //populate lists, some of the items in List2 (cat) will be in the List1 items Cats list
  
  //classes
  class pet{
     string ID;
     List&lt;cat&gt; Cats;
  }
  
  class cat {
     string ID;
     string name;
  }
  </code></pre>