如何设计一个支持在线答题中的游戏元素和关卡设计的系统

class User:
    def __init__(self, username, password, email):
        self.username = username
        self.password = password
        self.email = email

    def login(self):
        # 用户登录逻辑
        pass

    def register(self):
        # 用户注册逻辑
        pass

class Question:
    def __init__(self, content, options, answer):
        self.content = content
        self.options = options
        self.answer = answer

    def validate(self, user_answer):
        # 验证用户答案是否正确
        pass

class Game:
    def __init__(self, user, question):
        self.user = user
        self.question = question

    def start(self):
        # 游戏开始逻辑，包括计分、奖励等
        pass

class Level:
    def __init__(self, questions):
        self.questions = questions

    def add_question(self, question):
        self.questions.append(question)

    def remove_question(self, question):
        self.questions.remove(question)

    def update_question(self, question):
        # 更新问题
        pass

def main():
    user = User("testuser", "password", "testuser@example.com")
    question = Question("2 + 2 = ?", ["A. 1", "B. 2", "C. 3", "D. 4"], "D")
    game = Game(user, question)
    game.start()

if __name__ == "__main__":
    main()