anchor.diff:  class ProblemManager {
     JsonFile _dataFile;
   
  +  HashMap<int, List<ProblemItem>> _problems;
  +
     ProblemManager() {
  +    _problems = new HashMap<int, List<ProblemItem>>();
       _dataFile = ResourceManager.sample;
   
       _dataFile.onLoad().then((e) {
  -      log.info(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 {
  -  Sprite _question;
  +  String _question;
   
     List<String> _questions;
   
  
positive.code:   int getAnswer() {
      return _answer;
    }
  }
  
negative.code: 
    ProblemItem(this._question, this._questions, this._answer);
  
    String getQuestion() {
      return _question;
    }
  
  