c#程序问题

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 WinDemo
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            this.Load += Form1_Load;
        }
        List persons = new List();
        void Form1_Load(object sender, EventArgs e)
        {
            persons.Add(new Person() { Name = "顾若尘", Age=20, Phone="312321321" });
            persons.Add(new Person() { Name = "史进", Age = 19, Phone = "312321321" });
            persons.Add(new Person() { Name = "陈新", Age = 21, Phone = "312321321" });
            persons.Add(new Person() { Name = "田三", Age = 24, Phone = "312321321" });
            persons.Add(new Person() { Name = "李四", Age = 18, Phone = "312321321" });
        }
        class Person
        {
            public string Name { get; set; }
            public int Age { get; set; }
            public string Phone { get; set; }
        }
        private void button1_Click(object sender, EventArgs e)
        {
            this.dataGridView1.DataSource = persons;
        }

        private void button2_Click(object sender, EventArgs e)
        {
            var query = persons.Where(p => p.Age >= 19 && p.Age <= 20).ToList();
            this.dataGridView1.DataSource = query;
        }

        private void button3_Click(object sender, EventArgs e)
        {
            var query = persons.Where(p => p.Name.Contains("顾")).ToList();
            this.dataGridView1.DataSource = query;
        }
    }
}