This's a pen and that's a ruler.be 动词在什么情况下可以缩写什么时候不可以?

teacher:Hi,anna,are these your pencils? anna:no,they are bob's. teacher:and is this his green pen? anna:no,it isn't.the blue pen is his. teacher:what about this dicionary? anna:it's helen's.and the green pen is hers,too. teacher:and the eraser?is tha This pen are Amy and Sandy's还是This pen are Amy's and Sandy's this’s a pen and that’s a ruler.哪里错了 This's a red pen怎么改错? ()this()English?__It's,a,pen This is a pen and that’s an eraser.可不可以写成This is a pen and that is an eraser.呢? This's a pen and that's a ruler.be 动词在什么情况下可以缩写什么时候不可以? What's this?——___.(①It's a pen.②This is pen.③This is an pen.④It's a pen.) This is a pencil and a pen还是These are a pencil and a pen What's this?It's a pen.(改为复数句) Look at this.What's this in English,do you know?Ah,it's a photo.Who's tha This is a pen and ____ is a pencil. This is a pen,and ____is a pencil over there This is Peter's pen and that is ( )pencil,( )a red pencil.(he) 用适当形式填空 --It's a ball pen,( --It's a pencil.A.what is this B.and what is this C.what's it--It's a ball pen,( --It's a pencil.A.what is this B.and what is this C.what's it 英语翻译46A DOCUMENTS REQUIRED BENEFICIARY'S SIGNED COMMERCIAL INVOICE IN(1) ORIGINAL AND(2)COPIES.ESTABLISHED IN THE NAME OF:(APPLICANT WITH FULL NAME AND ADDRESS)THIS INVOICE MUST BEAR BENEFICIARY'S DECLARATION READING AS FOLLOWS:WE CERTIFY THA what's this in english a.It's pen b.It'sa pen c.I like pen 选哪个为什么? what's this?It's a pen.为什么不能说是this is a pen.我们老师说就是不能说this is a pen.为什么