Step 1: Locate the relative clause — "who always _______ the class every morning." The adverb "always" combined with "every morning" signals a habitual present action. Use present simple third-person singular: "greets". Step 2: Locate the main clause — "suddenly _______ silent when the teacher entered the room yesterday." The time signal "yesterday" and the past tense verb "entered" both confirm the action happened in the past. The simple past of "fall" is "fell". Step 3: Confirm the sentence is consistent — habitual present in the relative clause, past event in the main clause, matching the narrative logic. Answer: greets / fell