preservative

a. 保存的,有保存力的,防腐的
n. 预防法,预防药,防腐剂

For the first, the best preservative to keep the mind in health, is the faithful admonition of a friend.

说到第一种，最能保人心神之健康的预防药就是朋友的忠言规谏。

Salt is a common food preservative.

盐是一种常用的食物防腐剂。