1、because of losing a borrowed book。dear frank：i am terribly sorry to tell you that i have lost the valuable book you were so kind to lend me last week。i read it everyday and intended to finish it next month。last night when i came to my room，it was nowhere to be found。i will try to recover it as soon as possible。if i fail to find it，i will get a new book for you。old books are like old friends