您可以不投，因为它们是不同的类型。你有两个选择：

You can't cast because they are different types. You have two choices:

1）改变类，这样PersonWithAge从人继承

1) Change the class so that PersonWithAge inherits from person.

class PersonWithAge : Person
{
        public int Age { get; set; }
}

2）创建新的对象：

2) Create new objects:

IEnumerable<Person> p = pwa.Select(p => new Person { Id = p.Id, Name = p.Name });