title: How to search from a list inside a dictionary<string, List<string>>
body: <p>if I have a dictionary
      <code>&lt;string, List&lt;string&gt;&gt;</code>. (ex. &lt;12345, List&lt;"ABC", "456", "123">>
  and I want to pull out the key '12345' where I have "456" in the list of strings for each entry in the list.
  So my result would be another list.
  Wouldn't this be done with a linq statement?</p>