Jidesh Baidya

 Concrete class must not be dependent on each other This is called low couplings. It is good. High coupling is bad Using system;   Namespace coupling {  Class program   {       Static void main(string[] args)       {         Console.writelinw("hello world");         }      } Public class UserInterface  { Public void GetData() { Console.write("enter your username"); Var userName = console.readLine(); Console.write("enter your password"); Var password = console.readLine(); IBusines business= new Business(); business.SignUp(userName, password); } } Public class Business : IBusines { Public void SignUp(string userName, string password) { // validation  Var dataAccess = new DataAccess(); DataAccess.Store(userName, password); } } Public class BusinessV2 : IBusiness { Public void SignUp(string userName, string password) { // validation  Var dataAccess = new DataAccess(); Data...