Write an e-mail to your friend requesting him to return the book immediately.
From : email@example.com
To : firstname.lastname@example.org
Sent : Friday, October 12, 2015; 7:00 p.m.
Subject : Returning the book.
It is pretty long time you borrowed a book entitled “Comprehensive English Grammar and Composition” from me but you have not yet returned it to me. Perhaps you have forgotten it. However, my final exam. is knocking at the door. So, I have to study more and more. So, I need it badly. Please return the book as early as possible.
Your loving friend,