Something about the Internet

We are all busy talking about and use the Internet 1.__which set up in the 1960s.At first.the Internet was 2.__only used by the government,but in the early 1970s, 3.__the universities,hospitals and banks were allowed to use 4.__them too.However,computers were still very expensive 5.__and the Intemet was difficulty to use.By the start of 6.__