未能找到类型或命名空间名称“Student”(是否缺少 using 指令或程序集引用?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ch05.Examples
{
    class SortedDictionaryExample
    {
        StringBuilder sb = new StringBuilder();
        public SortedDictionaryExample()
        {
            SortedDictionary<int, Student> students = new SortedDictionary<int, Student>()
            {
                {2,new Student {Name="李四",Gender="男"}},
                {1,new Student {Name="张三",Gender="男"}},
                {3,new Student {Name="王五",Gender="男"}}
            };
            foreach(var v in students)
            {
                sb.AppendLine(string.Format("编号:{0}--姓名:{1},性别:{2}",v.Key,v.Value.Name,v.Value.Gender));
            }
        }
        public string GetOutPut()
        {
            return sb.ToString();
        }
    }
}