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We present a question answering (QA) system which learns how to detect and rank answer passages by analyzing questions and their answers (QA pairs) provided as training data. We built our system in only a few person-months using off-the-shelf components: a part-of-speech tagger, a shallow parser, a lexical network, and a few well-known supervised learning algorithms. In contrast, many of the top TREC QA systems are large group efforts, using customized ontologies, question classifiers, and highly tuned ranking functions. Our ease of deployment arises from using generic, trainable algorithms that exploit simple feature extractors on QA pairs. With TREC QA data, our system achieves mean reciprocal rank (MRR) that compares favorably with the best scores in recent years, and generalizes from one corpus to another. Our key technique is to recover, from the question, fragments of what might have been …