int num = 0;        private void button1_Click(object sender, EventArgs e)        {            num += 1;            string[] str1 = new string[] { "A", "B", "C" };            string[] str = new string[6];            str[0] = "AA";            str[1] = "BB";            str[2] = "CC";            str[3] = "DD";            str[4] = "EE";            str[5] = "FF";            Random r = new Random();            int j = r.Next(0, str.Length - 1); //r.Next(最小,最大)  返回一个指定范围内的数            label1.Text = "第"+num.ToString()+"次 ：" + str[j];        }