Choose the correct words or phrases that best complete the passage.

A major revolution for the automated office is electronic mail. The customary (16) ________system requires message written on paper to be(17) ______ physically from one location to another. With electronic mail, messages are converted (18) _______ electronic signals, tranmitted (19) ___________ in the world, and then changed back into the original written form, all in several seconds and minutes at (20) ________ .

Through the use of video screens in company offices, a single (21) _________ can be transmitted to hundreds of people in dozens of branch offices at the same time. Thus, electronic mail, along with (22) ________ , can be animportant asset in teleconferences. Furthermore, the use of electric mail in the form of a 'mailbox' (23) _________ to a telephone is also of great value.

Since in offices many telephone (24) __________ go uncompleted on the first attempt, with electronic mail, two-way conversion is not essential, so it

(25) _______ telephone use and saves time.

The Mayan Indians ________ an accurate and sophisticated calendar more than seven centuries ago.