ASP.NET WebForm 根据请求显示 不同的页面（类似PHP的include）

protected void Page_Load(object sender, EventArgs e)
{
    var area = Request.QueryString["id"].ToUpper();
    if (area == "Z")
    {
        StringWriter writer = new StringWriter();
        Server.Execute("z.aspx", writer);
        String html = writer.ToString();
        Response.Write(html);
    }
    else
    {
        StringWriter writer = new StringWriter();
        Server.Execute("area.aspx", writer);
        String html = writer.ToString();
        Response.Write(html);
    }
     
}