using System;
namespace ConsoleApp1
{

class Program1
{
    static void Main(string[] args)
    {
        Person objPerson = new Person("312");
        
        objPerson.Display();
        Student objPerson1 = new Student("123");
        objPerson1.Display();
        objPerson1.Display1();
    }
}

public class Person
{
    private string _id;
    public string Id
    {
        get { return _id; }    //get访问器，得到身份证号码字段的值
        set { _id = value; }    //set访问器，设置身份证号码字段的值
    }
    public Person()
    { }
    public Person(string id)
    {
        _id = id;
    }
    public void Display()
    {
        Console.WriteLine("{0}是" , this._id);
    }
}
public class Student : Person
{
    private string _id;
   
    public Student(string id)
    {
        _id = id;
    }
    public void Display1()
    {
        Console.WriteLine("{0}是1", this._id);
    }
}

}

你想打印出什么？你子类的构造函数里的参数 id 压根也没传给父类啊，父类里的 _id 不还是初始值？