Select Same Value on Multiple DropDowns in ASP.NET

I have three DropDown List Controls.each dropdown contains the static values 1,2,3,4 what i need to do is when a item is selected on the first dropdown(on SelectedIndexChanged Event) same items should be selected in other two dropdowns.

aspx code.

<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddl_SelectedIndexChanged">

    <asp:ListItem Text="1" Value="1" />

    <asp:ListItem Text="2" Value="2" />

    <asp:ListItem Text="3" Value="3" />

    <asp:ListItem Text="4" Value="4" />

</asp:DropDownList>

<asp:DropDownList ID="DropDownList2" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddl_SelectedIndexChanged">

    <asp:ListItem Text="1" Value="1" />

    <asp:ListItem Text="2" Value="2" />

    <asp:ListItem Text="3" Value="3" />

    <asp:ListItem Text="4" Value="4" />

</asp:DropDownList>

<asp:DropDownList ID="DropDownList3" runat="server" AutoPostBack="true" OnSelectedIndexChanged="ddl_SelectedIndexChanged">

    <asp:ListItem Text="1" Value="1" />

    <asp:ListItem Text="2" Value="2" />

    <asp:ListItem Text="3" Value="3" />

    <asp:ListItem Text="4" Value="4" />

</asp:DropDownList>

In the code behind add below

protected void ddl_SelectedIndexChanged(object sender, EventArgs e)

{

    DropDownList ddl = (DropDownList)sender;

    string value = ddl.SelectedValue;

    SetValue(DropDownList1, value);

    SetValue(DropDownList2, value);

    SetValue(DropDownList3, value);

}

protected void SetValue(DropDownList ddl, string value)

{

    ddl.SelectedIndex = ddl.Items.IndexOf(ddl.Items.FindByValue(value));

}