Answer:
the celebratory dinner
Explanation:
the sentence is basically about the dinner, and roast beef & mashed potatoes is what the subject (the celebratory dinner) <em>is.</em>
Dont add comma is the right one
Observations (what you see that is important for a possible future inference) 1. Heard a siren 2: Smelled smoke
Inferences: Kristens house catches on fire and turns off the fire alarm.