A:氧气
B:氮气
C:水蒸气
D:二氧化碳
We don't have enough nurses to look after the patients. At least _____ are needed.
找出划线的字的反义词。
①小白兔弯着腰在山坡上割草。____
②燕子为什么要低飞?____
我们的生活只需要阳光 ,不需要空气和水。( )