private void button1_Click(object sender, EventArgs e)
        {
            //你的字符串是用换行符作为分隔符,所以用Environment.NewLine
            string[] values = this.textBox1.Text.Split(new string[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
            StringBuilder sb = new StringBuilder();
            foreach(string value in values)
            {
                if (value.StartsWith("111") || value.StartsWith("000") || value.StartsWith("996"))
                {
                    sb.Append(value).Append(Environment.NewLine);
                }
            }
            this.textBox2.Text = sb.ToString();
        }