问从c#组合框的Access表中返回ID值的有效方法

EN

private void Form1_Load(object sender, EventArgs e)
{
    Book myBook = new Book;
    myBook.Connect();
    comboBox1.DataSource=myBook.IDs();
}

class Book
{
    OleDbCommand Comm;
    OleDbConnection Conn;
    OleDbDataReader Reader;
    string queryString;

    public void Connect()
    {
        Conn = new OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=D:\Book.accdb");
    }

    public List<string> IDs()
    {
        string singleID = null;
        List<string> IDs = new List<string>();
        queryString = "Select bID from Books";
        Comm = new OleDbCommand(queryString, Conn);
        Reader = Comm.ExecuteReader();
        while (Reader.Read())
        {
            singleID = Reader[0].ToString();
            IDs.Add(singleID);
        }
        Conn.Close();
        Reader.Close();
        return IDs;
    }
}