<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" OnSelectedIndexChanged="GridView1_SelectedIndexChanged"
            Width="516px">
            <Columns>
                <asp:TemplateField ShowHeader="False">
                    <ItemTemplate>
                        <asp:LinkButton ID="LinkButton1" runat="server" CausesValidation="False" CommandName="Select"
                            Text="向上"></asp:LinkButton>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField ShowHeader="False">
                    <ItemTemplate>
                        <asp:LinkButton ID="LinkButton2" runat="server" CausesValidation="False" CommandName="Select"
                            Text="向下"></asp:LinkButton>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:BoundField DataField="cid" HeaderText="编号" />
                <asp:BoundField DataField="cname" HeaderText="内容" />
            </Columns>
        </asp:GridView>

在这个GridView控件中有两个LinkButton
我想知道，怎么能在GridView1_SelectedIndexChanged事件中判断我点击的是哪一个LinkButton 呢？