When I review my flashcards, I review in batches of 50, from a flashcard library of 600 or so. My problem is that the batches keep repeating the same cards and not introducing the rest of the library. So I've quizzed 20-30 times from the same library, but still have several hundred cards that haven't been used. How can I make sure that the quizzing process presents me a broader selection of my library and make it repeat less? I'm sure that one of the settings is to blame, but I don't know which one. Help, please.