为什么出错，

为啥出错，，
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Chapter9
{
    class Class1
    {
        private string[] students = { "Tom", "Alice", "Jack" };
        static void Main()
        {
            var obj = new ClassExample16();
            for (int i = 0; i < obj.students.Length; i++)
            {
                Console.WriteLine(obj[i]);
                Console.ReadKey();
            }
        }

    }

    class classexample16
    {
        public string[] students = { "Tom", "Alice", "Jack" };
        public string this[int studentNo]
        {
            get
            {
                return students[studentNo];
            }
            set
            {
                students[studentNo] = value;
            }
        }
    }
}

编译后，错误1“Chapter9.ClassExample16.students”不可访问，因为它受保护级别限制E:\CSharp4_DefinitiveGuide_Source4\Chapter9\Class1.cs1437Chapter9

[解决办法]