pigs cows cats ducks rabbits sheep
My uncle has a farm. It's big. On the farm, you can see two ____ . There are twenty ____ and eighteen ____ on the farm. You can see eleven ____ , thirteen____ and fifteen____ .
自来水消毒过程中通常会发生化学反应,其反应的微观过程可用如图表示:
通过呼吸运动,肺实现了与外界环境的气体交换.下列关于平静呼吸的表示,正确的是( )