Which of the following can be copyrighted?

The reason source code can be copyrighted is that it is considered a form of expression, created by an author, and falls under the category of literary works. Copyright law protects original works of authorship fixed in a tangible medium of expression, and source code, being written in a programming language, fulfills these criteria. This means that a developer has exclusive rights to reproduce, distribute, and create derivative works based on their source code.

In contrast, facts and figures, scientific principles, and mathematical formulas do not meet the requirements for copyright protection because they are considered ideas, concepts, or general knowledge rather than original expressions. Copyright does not extend to mere facts or the underlying theories behind them since they belong to the public domain and can be utilized by anyone without infringement. Thus, the creative aspect that allows for copyright protection is absent in those other options, reinforcing the validity of source code as the only copyrightable material in the provided choices.