This is that they all want to but it.
A. a so useful book
B. such an useful book
C. a such useful book
D. so useful a book
网友回答
A. a so useful book
B. such an useful book
C. a such useful book
(答案→)D. so useful a book
解析：such a/an +形容词+名词=so +形容词+a/an +名词。