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。but i am afraid it can never take the place of the old one。 old books are like old friends。 once lost， they can never be replaced。 they are connected with cherished associations which the new ones can never have。 and for this irrecoverable loss， i am to blame。 i was so careless with my things。 this is a warning to me to be more careful in the future。yours truly，tom。

　　2、亲爱的弗兰克：很抱歉，上星期您借给我的那本书竟遗失了。我每一天都在看，准备下个月看完。昨晚我回到我的卧室，到处也找不到那本书。我将尽力找到它。万一找不到，我只好买一本新的还您。但是，新书恐怕不能代替那本旧书吧！旧书跟旧友一样，一旦失去就不能再得。旧书与往事相连，这种不可弥补的损失，皆由我起。我对待一切太大意了，这次给我一个警告，叫我以后要留意。