The book costs him 50 yuan.(保持原意不变)
问题描述：
The book costs him 50 yuan.(保持原意不变)
答
It costs hime 50 yuan to buy the book.
答
The book costs him 50 yuan.(保持原意不变)
He spends 50 yuan on the book
或者
He paid 50 yuan for the book
spend 钱on sth=pay……for=……cost
答
He pays 50 yuan for the book.
He spends 50 yuan to buy the book.