An Idea or Algorithm for displaying questions based on difficulty and user responses (C#) -

i'm trying create algorithm display set of questions user starting lowest difficulty , progressing difficulty level user answers questions correct , falling on difficulty level if user answers question wrong. haven't started code yet head start on how should tackle approach. general question model following.

    public class question     {         public int questionid { get; set; }         public string questiontext { get; set; }         public int difficulty { get; set; } //can range 1 5     } 

any suggestions on start?

public class question {     public int questionid { get; set; }     public string questiontext { get; set; }     public int difficulty { get; set; } //can range 1 5 }  public class user {     public string name { get; set; }      public int currentdifficulty { get; set; }     public question current { get; set; }     public hashset<question> answered { get; set; } }  public class questiondata {     private random rnd = new random();      public list<question> questions { get; private set; }      public void load()     {         questions = new list<question>();          // load question data  database or file     }      public question getnextquestion(user user)     {         list<question> possible = (from e in questions e.difficulty == user.currentdifficulty && !user.answered.contains(e) select e).tolist();         return possible.count == 0 ? null : possible[rnd.next(possible.count)];     } }