父类：

 class Person
    {
        public Person()
        {
            Console.WriteLine("========================");
        }

        public Person(string name, int age, string email)
        {
            this.Name = name;
            this.Age = age;
            this.Email = email;
        }

        public string Name { get; set; }
        public int Age { get; set; }
        public string Email { get; set; }
    }

子类：

 class Teacher : Person
    {
        public Teacher(string name, int age, string email, double salary)
            : base(name, age, email)
        {
            //this.Name = name;
            //this.Age = age;
            //this.Email = email;
            this.Salary = salary;
        }
        public double Salary { get; set; }
    }

这样是调用父类中第二个有参的构造函数，如果去掉Base默认调用无参构造函数

注意执行顺序是:先调用父类的构造函数，然后再执行子类自己的构造函数。