Final answer:
JavaScript is the best choice for adding interactive elements to a website, as it is the standard programming language for creating dynamic user interfaces in web browsers.
Step-by-step explanation:
The most suitable programming language for adding interactive elements to a website is D) JavaScript. This language is specifically designed to enable interactivity on web pages, allowing for the creation of dynamic and responsive user interfaces. While Python and Java are powerful programming languages, they are more commonly used for server-side or stand-alone applications, not for in-browser interactions. HTML is not a programming language but a markup language used to structure content on the web.