winform中textbox提示框

在winform中向textbox输入内容时下面有提示信息，效果如图所示：

        private void Form1_Load(object sender, EventArgs e)
        {
            AutoCompleteStringCollection strings = new AutoCompleteStringCollection();
            strings.Add("A1");//不区分大小写
            strings.Add("A2");
            strings.Add("Aas");
            strings.Add("B1");
            strings.Add("Beijing");
            strings.Add("bb-cims");
            textBox1.AutoCompleteCustomSource = strings;
            textBox1.AutoCompleteSource = AutoCompleteSource.CustomSource;
            textBox1.AutoCompleteMode = AutoCompleteMode.Suggest;
        }