遍历panel按钮依次显示

需求 panel1上有 button1,button2,button3，button4 三个按钮，集合list里面有（button3,button5……）等好多button；为button1增加click事件，遍历list 然后 每隔1秒button2,button3 依次出现,点击button4时，暂停显示，单击button1 从显示位置开始继续显示；目前代码，求修改：
 private void button1_Click(object sender, EventArgs e)
        {
            List<string> cs=new List<string>();
            cs.Add("button4");
            cs.Add("button5");
            for (int i = 0; i<cs.Count;i++ )
            {
                string b= cs[i];
                new Thread(new ParameterizedThreadStart(show)).Start(b);
            }
           
        }
        private delegate void SetSafeTree();
        public void show(object a)
        {
            foreach (Control c in this.panel1.Controls)
            {
                if (c is Button)
                {
                    if (c.Name.Equals(a))
                    {
                        if (c.InvokeRequired)
                        {
                            SetSafeTree call = delegate()
                            {
                                c.Visible = true;
                            };
                            c.Invoke(call);
                            System.Threading.Thread.Sleep(1000);
                        }
                    }
                   
                    
                }
            }
        }