Final answer:
option b,JavaScript is the programming language that adds interactivity to websites, distinct from HTML, Ruby, and C++ which have different primary uses.
Step-by-step explanation:
The programming language that adds interactivity to websites is JavaScript. HTML is a markup language used for structuring the content of a webpage. While it allows for the creation of static web pages, it doesn't provide interactivity. Meanwhile, JavaScript is a scripting language that runs on the client-side and allows for dynamic and interactive elements on websites.
For example, JavaScript can be used to create dropdown menus, validate form inputs, or display animations on a webpage. It can respond to user interactions, such as button clicks or mouse movements, and update the page accordingly.
On the other hand, Ruby and C++ are general-purpose programming languages that can be used for a wide range of applications, but they are not specifically designed for web development.