memento|mementos

那件旧毛衣对她来说就像玛德琳蛋糕，让她想起了大学时光。

The old sweater served as a ___memento, reminding her of her college days.

我把旅行时买的明信片当作纪念品保存起来。

I keep the postcards I bought during the trip as ___mementos.

我把这颗贝壳留作我们海滩之旅的纪念品。

I kept this shell as a ___memento of our beach trip.