Dear Professor Thomas,I appreciate that you have lent me one of your precious books.I am writing to ask whether I could keep it for a few days more,and to make a sincere apology for the delay.For a deeper understanding of it,I have been consulting so large amounts of reference sources that it takes much more time than expected,and now it seems impossible for me to finish it as scheduled.Moreover,it is not yet available in China whereas it's one of the important reference documents for my paper.For these reasons,I want to ask if I could have your permission to.return it two weeks later.Looking forward to your reply.Yours sincerety,Li Ming
