CS1936 C#找不到源类型“”学生“”的查询模式的实现。“找不到“‘Where”

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

namespace MyNamespace
{
    class Program
    {
        static void Main(string[] args)
        {
            List<Student> students = new List<Student>
            {
                new Student { Name = "Alice", Age = 20 },
                new Student { Name = "Bob", Age = 22 },
                new Student { Name = "Charlie", Age = 18 }
            };

            var filteredStudents = students.Where(s => s.Age > 20);

            foreach (var student in filteredStudents)
            {
                Console.WriteLine(student.Name);
            }
        }
    }

    class Student
    {
        public string Name { get; set; }
        public int Age { get; set; }
    }
}