P119-11-03-2021 - Abstract,sealed.Interface https://www.w3schools.com/cs/cs_abstract.asp https://www.geeksforgeeks.org/c-sharp-abstract-classes/ https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/sealed https://www.tutorialsteacher.com/csharp/csharp-interface#:~:text=In%20C%23%2C%20an%20interface%20can,functionalities%20for%20the%20file%20operations. Tapshiriq: Abstraction misal yazmaq