how to insert month in grid view

protected void Button1_Click(object sender, EventArgs e)
{
    List<string> test = new List<string>();
    test.Add(DropDownList1.SelectedValue + " ,  " + DropDownList2.SelectedValue);
   GridView1.DataSource = test;
    GridView1.DataBind();
    ((Label)GridView1.Rows[0].Cells[0].FindControl("Label2")).Text = test[0];
}

<div>
       <asp:DropDownList ID="DropDownList1" runat="server">
           <asp:ListItem>January</asp:ListItem>
           <asp:ListItem>February</asp:ListItem>
           <asp:ListItem>March</asp:ListItem>
           <asp:ListItem>April</asp:ListItem>
       </asp:DropDownList>
       <asp:DropDownList ID="DropDownList2" runat="server">
           <asp:ListItem>January</asp:ListItem>
           <asp:ListItem>February</asp:ListItem>
           <asp:ListItem>march</asp:ListItem>
           <asp:ListItem>april</asp:ListItem>
       </asp:DropDownList>
   </div>
   <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />
   <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False">
       <Columns>
           <asp:TemplateField>
               <ItemTemplate>
                   <asp:Label ID="Label2" runat="server" ></asp:Label>
               </ItemTemplate>
           </asp:TemplateField>
       </Columns>
   </asp:GridView>