title: what is green threading?
body: <p>What is green threading means in ruby on rails , what it actually do? 
   Is it a. " A design where fixed size pool of threads is shared around the program?"
         b. "when threads are emulated by virtual machine or interpreter?" or 
         c. " where program run accross the multiple CPU?"</p>
  
  <p><strong>Please explain with right ans?</strong>  </p>