What's wrong with this C# connection?

[Arielle]

Please tell me what's wrong with this picture.

 
public class MyClass
    {
        SqlConnection       ConnectionSql = null;
        SqlCommand          CommandSql = null;
        SqlDataReader         QueryResult = null;
 
        public MyClass(string dbString)
        {
            ConnectionSql = new SqlConnection(dbString);
            CommandSql = ConnectionSql.CreateCommand();
            CommandSql.Connection = ConnectionSql;
        }
 
 

public string ReturnSomething(string sql, int colIndex)
{
ConnectionSql.Open();
CommandSql.CommandText = sql;
CommandSql.Connection = ConnectionSql;
QueryResult = CommandSql.ExecuteReader();
return (QueryResult[colIndex].ToString());
}
}