Let the sky fall.和When the sky falls.为什么fall一个不加s一个加s?

Let the sky fall.和When the sky falls.为什么fall一个不加s一个加s? “Let the sky fall”怎么没有S? The sky looks blue.为什么looks要加s? what begins fall from the trees.begin为什么加s 英语谜语题 It's fall from the sky.It's cool. It'( ) Until The Stars Fall From The Sky Which, I fall from the sky,I have a pair of catch people's e When snow falls,it comes down from the sky.为什么用falls , Look!There are thounds of stars in the sky.为什么star可以加S? Look!There are thousands of stars in the sky.为什么star可以加S when the snow falls,为什么是 falls 而非 fall 或者……? what begins to fall from the thees?这个begin为什么加s