Perhaps not the hardest, but one where there's tons of room for improvement: the Story Cloze Test [1] is a test involving very simple, five-sentence stories, wh

Perhaps not the hardest, but one where there's tons of room for improvement: the Story Cloze Test [1] is a test involving very simple, five-sentence stories, where you pick the ending that makes sense out of two endings. A literate human scores 100% on this test. No computer system so far scores better than 60%. (And remember that random guessing gets 50%.) [1] http://cs.rochester.edu/nlp/rocstories/ http://cs.rochester.edu/nlp/rocstories/