In which stage of the plot can you use foreshadowing or flashback to add interest to your story?

Read the excerpt from david foster wallace’s infinite jest. my silent response to the expectant silence begins to affect the air of the room, the bits of dust and sportcoat-lint stirred around by the ac’s vents dancing jaggedly in the slanted plane of windowlight, the air over the table like the sparkling space just above a fresh-poured seltzer. the coach, in a slight accent neither british nor australian, is telling c. t. that the whole application-interface process, while usually just a pleasant formality, is probably best accentuated by letting the applicant speak up for himself. in this excerpt, the narrator is providing a, both objective descriptions and subjective commentaries. b. only objective information about people, setting, and events. c. only subjective responses to the things he sees and experiences. d. a compromised interpretation of events due to his unstable condition.