protected void Submit_Click(object sender, EventArgs e)
    {
        string arg = ((Button)sender).CommandArgument;
        if (arg.Equals("1"))
        {
            //抛出DivideByZeroException 异常
            int x = System.Convert.ToInt32(TextBox1.Text);
            int y = System.Convert.ToInt32(TextBox2.Text);
            int z = x / y;
            TextBox3.Text = z.ToString(); 
        }
        else if (arg.Equals("2"))
        {
            //抛出 ArgumentOfRangeException 异常
            throw new ArgumentOutOfRangeException("click?!");
        }
        else
        {
            //抛出异常
            throw new Exception("向上级传递异常"); 
        }
    }


//
string arg = ((Button)sender).CommandArgument;
        if (arg.Equals("1"))
这两句不懂，哪位大师给指导下啊，细点讲