如何在ASP.NET和C#中加载下拉列表？

<asp:DropDownList ID="DropDownList1" runat="server"></asp:DropDownList>

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        // 添加下拉列表项
        DropDownList1.Items.Add("选项1");
        DropDownList1.Items.Add("选项2");
        DropDownList1.Items.Add("选项3");
    }
}

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        // 创建数据源
        List<string> dataSource = new List<string>
        {
            "选项1",
            "选项2",
            "选项3"
        };

        // 绑定数据源到下拉列表
        DropDownList1.DataSource = dataSource;
        DropDownList1.DataBind();
    }
}

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        // 添加下拉列表项
        DropDownList1.Items.Add("选项1");
        DropDownList1.Items.Add("选项2");
        DropDownList1.Items.Add("选项3");

        // 设置默认选项
        DropDownList1.SelectedIndex = 0;
    }
}