The correct answer is (A) An extraordinary event. In science, an occurrence or event that can be observed or perceived, and can be described and explained in scientific terms. Something that is perceived by the senses, rather than by thought or intuition. Also, anything that impresses the observer as being remarkable.

Phenomenon comes from Latin phaenomenon, Greek phainomenon.

Examples of use:

• As much as he wanted to, he was unable to explain the phenomenon.
• The return of Haley's Comet was a phenomenon he would not see again.