选择B 因为宾语从句中 要用 陈述语序 你改的那个同义句 明显错了啊 也应是 how I can buy this book. 理由是 当主语一致时可省略 主语和情态动词 所以变成 how to buy this book
宾语从句要用陈述句语序。至于改同义句的问题,如果也是宾语从句的话,就该改成how i can buy this book,比如:can you tell me how to....?改为can you tell me how i can buy ....?