Task: Pos Tagging
Input (English): Sentence: " The Prophet 's guidance , " says Michael Scheuer , an al - Qaeda analyst who recently retired from the CIA and {{ once }} headed its Bin Laden unit , " was always , Before you attack someone , warn them very clearly ... " The anthrax mailings followed the pattern of letters they sent in January 1997 to newspaper branches in Washington , D.C. and New York City , as well as symbolic targets . 
Word: once
Output (English): ADV