am 做谓语是对于自身的表述 比如 I am a student.
is 做谓语是对于他（她、它）的表述 比如 He is a teacher.
are 是am 和 is 的复数形式,用于主语是we、they、there are是句型,表示有什么什么 比如 We are happy to see you.
There are four apples.
应该是是这样的吧