saliva

例句：

1. 1. Saliva is a natural substance secreted by the mouth.
   唾液是一种自然分泌的物质，由口腔产生。
2. 2. The taste of saliva can help us detect the presence of bacteria in our mouth.
   唾液的味道可以帮助我们检测口腔中细菌的存在。
3. 3. Saliva plays a crucial role in digestion and helps to break down food.
   唾液在消化过程中起着重要作用，有助于分解食物。