datalist中Itemplate如何控制其中一列的样式

前台的代码：<ul>
                            <asp:DataList ID="DataList1" runat="server" DataKeyField="id" DataSourceID="SqlDataSource1"
                                RepeatColumns="3" RepeatDirection="Horizontal">
                                <ItemTemplate>
                                    
                                    <li class="last"><a href="#">
                                        <img src="css/images/big1.jpg" alt="" /></a>
                                        
                                    </li>
                                </ItemTemplate>
                            </asp:DataList>
                            <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:NewConnectionString %>"
                                SelectCommand="SELECT * FROM [New]"></asp:SqlDataSource>
                        </ul>请看红色的class="last"
我的原意是最后的一项才加这个属性，之前的项是没有这个css设置的。。就是说前面的项：<li><a href="#">
                                        <img src="css/images/big1.jpg" alt="" /></a>
                                        
                                    </li>
在最后一项才添加这个class="last"
请问该如何控制？