When making Sichuan pickles, the mouth of the pickle jar should be sealed with water. The main purpose of this is (a) to prevent water evaporation and (b) to prevent fine particles.

Microbial fermentation plays an important role in food production. For example, lactic acid bacteria are used when making kimchi. Lactic acid bacteria are anaerobic bacteria. Under anaerobic conditions, lactic acid is produced by lactic acid fermentation, which makes vegetables present a special flavor without changing the quality of vegetables. Therefore, when making Sichuan pickles, the mouth of the pickle jar should be sealed with water to isolate the air and create an oxygen-free environment.

So choose: C.