如何在Linq C#中执行此操作

var result = from student in students
             where student.Age > 18
             select student;

students.ForEach(student => student.Age += 1);

students.RemoveAll(student => student.Name == "John");

var averageAge = students.Average(student => student.Age);

var result = from student in students
             join course in courses on student.Id equals course.StudentId
             select new { student.Name, course.CourseName };