Как заставить перебор вписывать все выбранные значения в textbox?

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        List<string> Perebor(GroupBox groupBox)
        {
            List<string> value = new List<string>();
            foreach (Control control in groupBox.Controls)
            {
                if (control.GetType() == typeof(CheckBox))
                {
                    CheckBox checkBox = (CheckBox)control;
                    if (checkBox.Checked == true)
                        value.Add(checkBox.Text);
                }
                else if (control.GetType() == typeof(RadioButton))
                {
                    RadioButton radioButton = (RadioButton)control;
                    if (radioButton.Checked == true)
                        value.Add(radioButton.Text);
                }
            }
            return value;
        }

        public Form1()
        {
            InitializeComponent();
        }
        private void button1_Click(object sender, EventArgs e)
        {
            foreach (string text in Perebor(groupBox1))
            { textBox1.Text = text; }
        }
    }
}