asp.net控件 gridview单击操作问题？

asp.net控件 gridview行中设置两个buttonfile按钮，“修改”和“删除”。如何在后台实现单击操作。代码如下：
前台：
<asp:GridView ID="GridView1" runat="server" OnRowCommand="GridView1_RowCommand" OnSelectedIndexChanged="GridView1_SelectedIndexChanged">
<Columns>
<asp:ButtonField ButtonType="Button" Text="修改" />
<asp:ButtonField ButtonType="Button" Text="删除" />
</Columns>
</asp:GridView>

后台：
protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
{

if (？？？？此处如何判断是修改按钮还是删除按钮)
{
//确定操作行的索引，转换格式并保存为index，
int index = Convert.ToInt32(e.CommandArgument);

// Retrieve the row that contains the button clicked
// by the user from the Rows collection.
//将GridView1的索引行提取出来，赋给row