• "Study the examples below to see how adverb clauses are reduced:

  1. Time sequences with after, before, once, since, until, when, and while: 
  
  After they sang two songs, the performers did a dance. [clause] 
  After singing two songs, the performers did a dance. [phrase] 
  
  Before he answered the phone, he grabbed a pencil and notepad. [clause] 
  Before answering the phone, he grabbed a pencil and notepad. [phrase] . . . 
  
  2. Giving reasons with because 
  When a clause introduced by because is reduced, because is omitted and the verb changes form: 
  
  Because she had always been interested in sports, Linda became an avid supporter of the team. [clause] 
  Having always been interested in sports, Linda became an avid supporter of the team. [phrase] 
  
  3. Clauses of concession with although, despite, in spite of, though, andwhile: 
  
  Although he was hurt, Jack managed to smile. [clause] 
  Although hurt, Jack managed to smile. [phrase] . . . 
  
  In spite of the fact that she works long hours, Joan spends a lot of time with her family. [clause] 
  In spite of working long hours, Joan spends a lot of time with her family. [phrase] . . .

  The verb in a reduced adverb clause can be in one of two forms. The -ing form is used for the active voice, and the -ed form (the past participle) is used for thepassive voice."
  (Jolene Gear and Robert Gear, Cambridge Preparation for the TOEFL® Test, 4th ed. Cambridge University Press, 2006)



• While I was away in college, I stayed with my roommate's family during one spring break. [clause]
  While away in college, I stayed with my roommate's family during one spring break. [phrase]



• When she is working at home, Carla takes her youngest child to school in the morning. [clause]
  When working at home, Carla takes her youngest child to school in the morning. [phrase]



• Although Marc Bloch was impressed by the bravery of his fellow soldiers, he had harsh words for the army leadership. [clause]
  "Although impressed by the bravery of his fellow soldiers, Bloch had harsh words for the army leadership." [phrase]
  (Marnie Hughes-Warrington, Fifty Key Thinkers on History, 2nd ed. Routledge, 2008)
• Source:http://grammar.about.com/od/rs/g/Reduced-Adverb-ial-Clause.htm