There is a pen on the desk.如何解释句子结构?

there is a pen on the desk 变为复数 there is a pen on the table.pass_____to me plese. Look!There is a pen __(lie) on the ground. There is a pen on the desk 同义句转换 There is only a pen on the table=There is＿ ＿a pen on the table空里填什么? There is a pen on the desk.(对a pen 提问.)____________on the desk? there is a pen on the table;那there are pens on the table可以吗? there is a pen in my pencil-box.there is an apple on the table. There is a pen on the book?把on the book 划横线,变换句型. There ___ a pen and two pencils on the desk.用is还是are~There ___ a pen and two pencils on the desk.用is还是are~ is there a pen and some books on the desk?肯定回答是yes,there is 还是yes there are There is a pen and three apples on the desk.为什么用is不用are? there is a pen and some rubbers on the table.这里应该用is还是are? There is a book and a pen on the table改为复数句 i have got a postcard form my pen friend .there is a beautiful [ ]on it There is a book and a pen on the desk.(变为否定句) there is a pen and two books on the desk.还是there are a pen and two books on the desk?对这语法不懂,急用! there is not a pen on the desk… （a monththere is not a pen on the desk…（a month ago）改为过去式