Final answer:
The open-closed principle states that software entities should be open for extension but closed for modification. It encourages writing code that is easy to extend without modifications.
Step-by-step explanation:
The open-closed principle is a design principle in object-oriented programming. It states that software entities (classes, modules, functions, etc.) should be open for extension but closed for modification. This means that you should be able to add new functionality to a class without modifying its existing code.
For example, let's say you have a class that calculates the area of different shapes. If you want to add a new shape, like a triangle, you can extend the existing class by creating a new class that inherits from it and implements the necessary functionality for calculating the area of a triangle. This way, you don't need to modify the original class or any other classes that depend on it.
In the given options, the correct answer is a. modification/extension. The open-closed principle encourages you to write code that is easy to extend without the need for modifications.