the book is very hard to understand 为什么要用 to?

the book ____(it )is very interesting the book is very useful 感叹句 the book is very cheap同义句 I think the book is very good.____ ____ ____,the book is very good The book is very interesing.(对very interesing提问)（） is the book? The comic book is 3 yuan.It is very e_________ What he said was ok.句子结构划分 I know want it is The old man thinks he is Mymother works very har This is the very book that I lost yesterday. the a() of this book is a very young girl l want__(read)the book.lt is very interesting. the book ____ is very interesting everyone likes it I think the book is very( )(use的正确形式) the book is very （help）,do you think so? the book（）卖者 is a very young man This is the very book that belongs to this is the very book ___i am afterwhichthatwhosewhom The book On music is very useful是什么意思 Is the book i___?---Yes,I like it very much