Final answer:
To change the background and text colors on a website, it is best to use CSS for both site-wide and individual element changes because it maintains separation of content and design and simplifies maintenance.
Step-by-step explanation:
The best way to change background color and text color on a website is by using Cascading Style Sheets (CSS). When you need to apply styles to the entire website or to large portions of it, CSS is the preferred method. This approach keeps content and design separate, which is a best practice for web design. For example, to change the background color, you can use the background-color property, and to change the text color, the color property in your CSS.
Using CSS for these changes rather than HTML ensures that your code is cleaner and more maintainable. It allows you to make site-wide changes from a single location, which is more efficient and less error-prone than modifying individual HTML elements. Therefore, the correct answer to the question would be 'b) Regardless of how much of the site these changes should affect, it is best to define it in the CSS.'