The word "them” in paragraph 3 refers to _______.

Câu hỏi: Read the following passage and mark the letter A, B,C or D on your answer sheet toindicate the correct answer to each of the questions from 39 to 43.
It was widely reported last year that sales of guidebooks are falling fast, thanks to developments in the Internet and mobile phones. It makes sense. Why bother taking a heavy book with you when you can down all the information you need to your phone as you walk around the cathedral?
Writing a new book about a place is a rewarding job, but one that is becoming a rarity. Publishers are more concerned with keeping existing books up to date than bringing out new ones in an already crowded market. This is understandable, since every guidebook is actually out of date as soon as it is published. It may have been researched a year before being printed and it could have sat on the bookshop shelf for a year or two, so its information might be three years old by the time the reader uses it in practice. It is hardly surprising, therefore, that some publishers are inviting almost as much in updating and redesigning their books as they did creating them. Updating guides is nowadays a good way for new writers to get started.
But if the Internet via a mobile phone can deliver information just as well as printed paper but much faster, at almost no cost, is there a future for printed guidebook? Other books you read at home, but a travel guide's main purposes for urgent reference when you're desperate to find accommodation or somewhere to eat. Using a modern cellphone, any traveller can now enjoy a "paperless holiday". Want to know the opening times of the museum? Look them up online. Need some information on the ancient building you're standing in? Download it.
(Adapted from Cambridge FCE book)
The word "them" in paragraph 3 refers to _______.
A. purposes
B. books
C. times
D. guides