Iam Getting an error - "System.IndexOutOfRangeException: CountryID" Can Any One Tells What is the problem

public class ContinentDataAccessLayer
{
  public static List<continent> GetAllContinents()
  {
    List<continent> listContinents = new List<continent>();
    
    string CS = ConfigurationManager.ConnectionStrings["con"].ConnectionString;
    using (SqlConnection con = new SqlConnection(CS))
    {
      SqlCommand cmd = new SqlCommand("Select CountryName from country", con);
      con.Open();
      SqlDataReader rdr = cmd.ExecuteReader();
      while (rdr.Read())
      {
        Continent continent = new Continent();
        continent.ContinentId = Convert.ToInt32(rdr["CountryID"]);
        // System.IndexOutOfRangeException: CountryID
        continent.ContinentName = rdr["CountryName"].ToString();
    
        listContinents.Add(continent);
      }
    }

    return listContinents;
  }
}