fastadj.快的；迅速的；紧的；牢固的；放荡的adv.快速地；紧紧地；放荡地；深深地n.斋戒；禁食；系泊用具v.斋戒；禁食fastigian.病危时刻；高峰期；极度；顶点

1. The stomach acid helps digest what we eat.
   胃酸有助于消化我们吃的东西。
2. Why does stomach acid travel up the oesophagus?
   为什么胃酸会反流进食道呢？