title: Add elements from one list to another C#
body: <p>What is the simplest way to add elements of one list to another?</p>
  
  <p>For example, I have two lists:</p>
  
  <p>List A which contains x items
  List B which contains y items.</p>
  
  <p>I want to add elements of B to A so that A now contains X+Y items. I know this can done using a loop but is there a built in method for this? Or any other technique?</p>