anchor.diff:    int getAnswer() {
       return _answer;
     }
  +
  +  String toString() {
  +      return {
  +          "question": _question,
  +          "options": _questions,
  +          "anseer": _answer
  +      }.toString();
  +  }
   }
  
positive.code: 
    ProblemItem(this._question, this._questions, this._answer);
  
    Sprite getQuestion() {
      return _question;
    }
  
  
negative.code: class ProblemManager {
    JsonFile _dataFile;
  
    HashMap<int, List<ProblemItem>> _problems;
  
    ProblemManager() {
      _problems = new HashMap<int, List<ProblemItem>>();
      _dataFile = ResourceManager.sample;
  
      _dataFile.onLoad().then((e) {
          JsonList list = new JsonList.fromString(e['problems'].toString());
          for (JsonObject problem in list) {
              int level = problem.level;
              String question = problem.data.question;
              int answer = problem.data.answer;
              List<String> questions = problem.data.options;
  
              if (!_problems.containsKey(level)) _problems[level] = new List<ProblemItem>();
              List<ProblemItem> list = _problems[level];
              list.add(new ProblemItem(question, questions, answer));
              _problems[level] = list;
          }
          // log.info(_problems);
      });
    }
  }
  
  class ProblemItem {
    String _question;
  
    List<String> _questions;
  
  