在查询表达式中使用方法语法

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

namespace Linq_1
{
    class Program
    {
        static void Main(string[] args)
        {
            var studentQuery6 =
     from student in students
     let totalScore = student.Scores[0] + student.Scores[1] +
         student.Scores[2] + student.Scores[3]
     select totalScore;

            double averageScore = studentQuery6.Average();
            Console.WriteLine("Class average score = {0}", averageScore);
        }

        static List<Student> students = new List<Student>
{
   new Student {First="Svetlana", Last="Omelchenko", ID=111, Scores= new List<int> {97, 92, 81, 60}},//
   new Student {First="Claire", Last="O’Donnell", ID=112, Scores= new List<int> {75, 84, 91, 39}},
   new Student {First="Sven", Last="Mortensen", ID=113, Scores= new List<int> {88, 94, 65, 91}},
   new Student {First="Cesar", Last="Garcia", ID=114, Scores= new List<int> {97, 89, 85, 82}},
   new Student {First="Debra", Last="Garcia", ID=115, Scores= new List<int> {35, 72, 91, 70}},
   new Student {First="Fadi", Last="Fakhouri", ID=116, Scores= new List<int> {99, 86, 90, 94}},
   new Student {First="Hanying", Last="Feng", ID=117, Scores= new List<int> {93, 92, 80, 87}},
   new Student {First="Hugo", Last="Garcia", ID=118, Scores= new List<int> {92, 90, 83, 78}},//
   new Student {First="Lance", Last="Tucker", ID=119, Scores= new List<int> {68, 79, 88, 92}},
   new Student {First="Terry", Last="Adams", ID=120, Scores= new List<int> {99, 82, 81, 79}},//
   new Student {First="Eugene", Last="Zabokritski", ID=121, Scores= new List<int> {96, 85, 91, 60}},//
   new Student {First="Michael", Last="Tucker", ID=122, Scores= new List<int> {94, 92, 91, 91} }
};
    }
    /// <summary>
    /// 学生类
    /// </summary>
    public class Student
    {
        public string First { get; set; }//名
        public string Last { get; set; }//姓
        public int ID { get; set; }//编号
        public List<int> Scores;//分数
    }


}