2. The method of claim 1 , wherein: said picking comprises, for each given one of said words extracted in said extracting step, calculating a conditional probability of each given one of said words, given said base query, using said topic model of said corpus; and said adding comprises adding at least one of said words with a highest value of said conditional probability, and exceeding a first threshold to said base query to generate said first expanded query.
2. The method of claim 1 , wherein: said picking comprises, for each given one of said words extracted in said extracting step, calculating a conditional probability of each given one of said words, given said base query, using said topic model of said corpus; and said adding comprises adding at least one of said words with a highest value of said conditional probability, and exceeding a first threshold to said base query to generate said first expanded query. 3. The method of claim 2 , wherein said second expanded query is identical to said first expanded query.