"Is this book___ our Chinese teacher recommended to us? "
将其改成肯定句为：This is book___ our Chinese teacher recommended to us.
This is book是个完整的句子,后面跟的是同位语从句,而不是定语从句.所以选B.
若将句子改为：
Does this book____our Chinese teacher recommended to us?
就选A.