为什么“I bought a book ."变为疑问句时动词为原型“buy”

I bought a book for 为什么“I bought a book .变为疑问句时动词为原型“buy” I bought a book ( ) my friend recommended.是否填 that 或 which 都可以?为什么? Yesterday i bought a book.Books are not very expensive.请问为什么后一个book要加S.快.急 i bought a book three days ago.改为一般疑问句. i,bought,book,father,for,my,a.连词成句啊! I bought a-------(cook) book in bookstore.就填cook This is a book.I bought it.改为宾语从句 I bought a book _ 10 yuan填介词啊 this is a book which i bought yesterday为什么不是to which,而是which详细解释下 谢了 I bought him a book中的bought是什么系动词吗大神们帮帮忙 i bought this book ___ one yuan a copy.填ati bought this book ___ fifty cents.填for The book is a dictionary.I bought the book.改成定语从句 I bought him a book in a bookshop yesterday.改成强调句：It was him I bought a book in a bookshopyesterday.错的话错在哪里? 2.21I have bought this story book for more than ten years.have bought 错了应该改为?为什么? 英语多项选择 I lost the book I_____.I lost the book I _____．　A．have bought 　　　B．bought C．had bought D．had been bought写原因 yesterday i bought a book.the book is really hard to understand(合并为一句)yesterday i bought a book______ _______ really hard to understand I bought a storybook and a book of cartoons 对a storybook and a book of cartoons 提问