The correct answer is A. Flashback.
Step-by-step explanation
The flashback is a narrative device in which the author interrupts the narration to jump into the past through memory. This resource is also used in other fields such as cinema, series, comics, and video games. Therefore, the sentence "My dream began in a boring math class. I never liked numbers as they never made any sense to me" is a flashback since the character refers to an episode from his past through memory. So the correct respect is A.