public class Person {        public DateTime birth;        public DateTime? death;        string name;        public TimeSpan Age {            get {                if (!death.HasValue) {                    return DateTime.Now - birth;                }                else {                    return death.Value - birth;                }            }        }        //构造函数        public Person(string name, DateTime birth,DateTime?death) {            this.birth = birth;            this.death = death;            this.name = name;        }    }Person tr = new Person("AAAA", new DateTime(1988, 12, 13),null);            Person kk = new Person("BBBB", new DateTime(1912, 12, 13), new DateTime(1954, 12, 12));            Console.ReadKey();