title: Regular expression to find and remove duplicate words
body: <p>Using regular expressions in C#, is there any way to find and remove duplicate words or symbols in a string containing a variety of words and symbols?</p>
  
  <p><strong>Ex.</strong> </p>
  
  <p><strong>Initial string of words:</strong></p>
  
  <p>"I like the environment. The environment is good."</p>
  
  <p><strong>Desired string:</strong></p>
  
  <p>"I like the environment. is good"</p>
  
  <p><strong>Duplicates removed:</strong> "the", "environment", "."</p>