Task: Question Answering
Input (English): After excluding all the words that are not used by at least three separate users in our training set, we build our AllWords model by counting the frequencies of all the remaining words and training a multinomial Naive Bayes classifier.  
 Question: What model did they use for their system?
Output (English): AllWords model by counting the frequencies of all the remaining words and training a multinomial Naive Bayes classifier