Instruct: Classify Amazon reviews into positive or negative sentiment
Query: I enjoyed the book , but it was hard to understand.

I enjoyed this book called " The Wind in the Door."The book starts out in the twins'garden. The whole book is based on three people, Meg, Calvin and a cheribum. The conflict of this book is to save Charles Wallace. His sister tries to complete the two tasks before the faradolae stop deepening and singing the joyful song to the stars and the heavens. If the faradolae do not deepen and sing the joyful song, Charles will die. It is full of action , but hard to follow.