Part I includes the Pile of Done™, which allows you to retake every question you've answered correctly, either randomly from all categories or by focusing on questions from one category at a time.. The flashcard-like format infinitely serves up questions and your answers to these questions won't affect your statistics in any way. It's a nice way to brush up on questions you have answered correctly in the past - especially those you maybe haven't seen in some time. Just note that this feature is only unlocked once you've completed 80% of the questions in the program. So it's a little something to look forward to as you make your way through OptoPrep.
More generally speaking, an active subscription entitles you to access all questions in Practice Question and Timed Exam modes until you have answered each question correctly. Because your individualized statistics (which can provide valuable guidance in your studying) are based on your question history, we are unable to reset your question bank.
Once you have completed the program by answering all questions correctly, you continue to have access to all questions through your History pages. Therein, you will find a history of every question you have answered, including answer explanations. In this way, all of the material remains available to you for the duration of your subscription.