c# – 如何使IEnumerable只读？

class Person
    {
        public string FirstName = string.Empty;
        public string LastName = string.Empty;

        public Person(string firstName,string lastName) {
            this.FirstName = firstName;
            this.LastName = lastName;
        }
    }

    class List1
    {
        public List<Person> l1 = new List<Person>();

        public List1()
        {
            l1.Add(new Person("f1","l1"));
            l1.Add(new Person("f2","l2"));
            l1.Add(new Person("f3","l3"));
            l1.Add(new Person("f4","l4"));
            l1.Add(new Person("f5","l5"));
        }
        public IEnumerable<Person> Get()
        {
            foreach (Person p in l1)
            {
                yield return p;
            }

            //return l1.AsReadOnly(); 
        }

    }  

    class Program
    {

        static void Main(string[] args)
        {
            List1 list1Instance = new List1();

            List<Person> p = new List<Person>(list1Instance.Get());           

            UpdatePersons(p);

            bool sameFirstName = (list1Instance.l1[0].FirstName == p[0].FirstName);
        }

        private static void UpdatePersons(List<Person> list)
        {
            list[0].FirstName = "uf1";
        }
    }

我们可以通过更改List1.Get()的返回类型来更改此行为吗？

谢谢