A．ought
B．doubt
C．thought
D．bought

A．they cover major points of the book in detail
B．they may help reader to better understand the book
C．they can take readers a lot of time to read every part of the book
D．they may help the readers find the important parts of the book

A．to recommend a whole book for students to read
B．to require students to read carefully
C．to assign reading with a certain purpose
D．to locate, books for students to find