public static IEnumerable<Student> StudentsInAgeRange(Student[] students, int minAge, int maxAge)
        {
            var result =
                from student in students
                where student.Age >= minAge && student.Age <= maxAge
                select student;

            return result;
        }
        public static IEnumerable<Student> FirstBeforeLastName(Student[] students)
        {
            var result =
                from student in students
                where student.FirstName.ElementAt(0) < student.LastName.ElementAt(0)
                select student;

            return result;
        }