Final answer:
Alex's story was denied copyright because it lacked a fixed form, which means the creature idea was not expressed in a tangible medium, a requisite for copyright protection.
Step-by-step explanation:
Alex's science fiction story about half-living, half-robot creatures was denied copyright protection because it lacked a fixed form, which is one of the essential requirements for copyright eligibility. The lack of fixed form means that while the idea for the creatures may have been creative and original, it was not expressed in a tangible medium of expression, such as written down in a story or illustrated in drawings, which allows it to be perceived, reproduced, or communicated. Copyright law does not protect ideas, procedures, processes, systems, methods of operation, concepts, principles, or discoveries, regardless of how original or creative they may be unless they are fixed in a tangible form of expression.
On the other hand, a problem in a story, as described in the given reference from LibreTexts, refers to elements in the narrative that challenge readers' understanding or expectations, such as unexplained character behavior or narrative inconsistencies. These can be intentional devices used by the author to invite interpretation and deepen engagement with the text.