diff --git "a/\347\216\213\345\270\205/\347\273\203\344\271\2403.md" "b/\347\216\213\345\270\205/\347\273\203\344\271\2403.md"
new file mode 100644
index 0000000000000000000000000000000000000000..dea4c4b7956fe4d649db1f7bd1f2d8e3653fc768
--- /dev/null
+++ "b/\347\216\213\345\270\205/\347\273\203\344\271\2403.md"
@@ -0,0 +1,37 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Web;
+using System.Web.UI;
+using System.Web.UI.WebControls;
+
+namespace WebApplication1
+{
+    public partial class WebForm1 : System.Web.UI.Page
+    {
+        protected void Page_Load(object sender, EventArgs e)
+        {
+            if (!Page.IsPostBack) {
+                SqlDataSource1.SelectCommand = "select * from city where type=1 ";
+                SqlDataSource2.SelectCommand = "select * from city where type=2 and pid=2";
+                SqlDataSource3.SelectCommand = "select * from city where type=3 and pid in (select id from city where type = 2 and pid = 2)";
+            }
+
+        }
+    
+        protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
+        {
+        
+            SqlDataSource2.SelectCommand = "select * from city where type=2 and pid=" + DropDownList1.SelectedValue;
+            
+            SqlDataSource3.SelectCommand = "select * from city where type=3 and pid in "(select id from city where type = 2 and pid = " + DropDownList1.SelectedValue+")";
+        }
+    
+        protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
+        {
+        
+            SqlDataSource3.SelectCommand = "select * from city where type=3 and pid =" + DropDownList2.SelectedValue;
+            
+        }
+    }
+}
\ No newline at end of file