The Internet is a (66) network of networks which interconnects (67) ranging from the simplest personal computers to the most sophisticated mainframes and supercomputers. This network of networks is used for an extraordinary range of purposes - long distance collaborations, retrieving free software and documents, (68) library catalogs, (69) in t6 supercomputers - the list of current Internet activities and (70) is large and the range of possible future applications is as unlimited as our imagination.

A．worldwide

B．abroad

C．large

D．extensive