The “phenomenon” is something, which is critical but unusual aspect in representing that thing.
In case of scientific phenomenon, it is easier to obtain both testable hypotheses because both dependent & independent variables can be easily identified; finally investigator can design a study by reviewing literature review for experimental protocols, previous investigations to describe a “phenomenon based on hypothesis”.
Thus, the options (d), (b) and (a) are incorrect.
The “phenomenon” is something, which is critical but unusual aspect in representing that thing.
Therefore, the correct option is – c. Something that is significant but unusual.