题目内容：

微观经济两个选择题
According to the article,sales of a given textbook tend to fall in the semester before a new edition of the book is released because:
A.Professors tend to switch to textbooks that have been updated most recently
B.Students anticipate the decline in the resale value of a textbook that is up for revision
C.Students would rather wait and buy the latest edition
why would new textbook sales fall in the years following the release of the latest edition?
A.As the edition of the textbook ages,college libraries tend to hold fewer copies for check out.
B.More professors adopt the new edition of the textbook for their classes.
C.The pool of books in the used textbook market grows.
D.The expected resale value of the textbook increases