Несовместимость по доступности: доступность типа поля "System.Collections.ObjectModel.Collection" ниже доступно - C#

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;
using System.IO;
using System.Collections.ObjectModel;
 
namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Collection<Record> records = new Collection<Record>(); //ошибку выдает в это строке подчеркивая records
        StreamReader reader;
        StreamWriter writer;
        class Record
        {
            public String Name, date, za4;
        }
        
        public Form1()
        {
            InitializeComponent();
        }
      
        private void Form1_Load(object sender, EventArgs e)
        {
            LoadFromFile();
        }
        private void SaveToFile()
        {
            writer = new StreamWriter("data.txt");
            for ( int i = 0; i< records.Count; i++)
            {
                writer.WriteLine(records[i].Name);
                writer.WriteLine(records[i].date);
                writer.WriteLine(records[i].za4);
            }
            writer.Close();
        }
        private void LoadFromFile()
        {
            Record record;
            reader = new StreamReader("data.txt");
            while (!reader.EndOfStream)
            {
                record = new Record();
                record.Name = reader.ReadLine();
                record.date = reader.ReadLine();
                record.za4 = reader.ReadLine();
                reader.ReadLine();
                records.Add(record);
            }
            reader.Close();
        }
 
        private void Form1_Shown(object sender, EventArgs e)
        {
            FillListBox();
        }
        private void FillListBox()
        {
            listBox1.Items.Clear();
            for (int i = 0 ; i<records.Count; i++)
            {
                listBox1.Items.Add(records[i].Name + ' ' + records[i].date + ' ' + records[i].za4);
            }
            listBox1.Items.Add("(new)");
        }
 
          private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (listBox1.SelectedIndex < 0 ) return;
            if (listBox1.SelectedIndex < records.Count)
            {
                textBox1.Text = records[listBox1.SelectedIndex].Name;
                textBox1.Text = records[listBox1.SelectedIndex].date;
                textBox1.Text = records[listBox1.SelectedIndex].za4;
            }
            else
            {
                textBox1.Text= " ";
                textBox2.Text= " ";
                textBox3.Text= " ";
            }
        }
 
        private void button2_Click(object sender, EventArgs e)
        {
            if (listBox1.SelectedIndex< records.Count)
                records.Remove(records[listBox1.SelectedIndex]);
            SaveToFile();
            FillListBox();
 
        }
 
        private void button1_Click(object sender, EventArgs e)
        {
            if (listBox1.SelectedIndex == listBox1.Items.Count-1)
            {
                Record record = new Record();
                record.Name = textBox1.Text;
                record.date = textBox1.Text;
                record.za4 = textBox1.Text;
            }
            SaveToFile();
            FillListBox();
 
        }
            
    }
}