This is _most useful reference book I have on this subject.

This is _most useful reference book I have on this subject. “This is ______ most useful reference book,” a teacher from This is so useful a reference book ___we can use while study This is () useful story book.. This book is useful to me,so I _____ 20 yuan on it yesterday This is the best book ____ on the subject This is quite a useful book . This book is _______on the subject the subject is very well____in this book This is _____ useful book.I read _____ book every day. This is the best book that there is on the subject可以解释一下这个句子 this book is()on the subject.A.the much best B,much the best