用冠词a/ an或Be动词（am / is / are ）填空。
What’s this in English ?  It’s ________ pen.
Is that _________ orange?  No, it isn’t.
It is ________ ruler.
This is ________ key.
Frank ________ OK.
Eric  and Dave________ good friends.
What _______these?
How ________ your father?
I ________ a boy.
You ________ good.