All of us would have enjoyed the party much more if there ________ quite such a crowd of people there.
句意：如果那儿没那么多人，大家会更喜欢这次聚会的。本题考查语法，主句用了would have done，说明是虚拟语气，条件句应该用had done的形式。结合句意，选择C。