dropdown in asp.net

Question

I have three dropdown for Day,Month,Year

in each dropdown i added these lines of code

ddlDay.Items.FindByValue(System.DateTime.Now.AddDays(-1).Day.ToString()).Selected = true;

but i want to show it as

DD selected as in dropdown Day

MM selected as in dropdown Month

YYYY selected as in dropdown Year

I also use

<asp:DropDownList ID="ddlMonth" runat="server" class="form-control"> <asp:ListItem Value="-1">MM</asp:ListItem> </asp:DropDownList>

these lines to each drop down but it not working

Pls help me..Thanks in Advance