49.
Your Answer is
Correct Answer is A
Explanation
they had once been served... is an attributive clause that modifies meal.
Item A: the omission of that/which (principle: when that/which is used as an object in an attributive clause, it can be omitted), correct.
Item B/C: the perfect meal is a specific situation, so non-restrictive attributive clauses cannot be used here.
Item D: Make the two sentences before and after without conjunctions.