The ARPANET (66) ( the rules of syntax that enable computers to communicate on a network) were originally designed for openness and flexibility, not for (67) The ARPA researchers needed to share information easily, so everyone needed to be an unrestricted "insider" on the network. Although the approach was appropriate at the time, it is not one that lends itself to today’s commercial and government use.
As more locations with computers (known as (68) in Internet parlance)joined the ARPANET, the usefulness of the network grew. The ARPANET consisted primarily of university and government computers, and the applications supported on this network were simple: electronic mail ( E - mail), electronic news groups, and (69) connection to other computers. By 1971, the Internet linked about two dozen research and government sites, and researchers had begun to use it to exchange (70) not directly related to the ARPANET itself. The network was becoming an important tool for collaborative research.

A．safety

B．guard

C．attachment

D．security

在Excel中，选定一个单元格后按Del键，将备删除的是（）。

A.单元格

B.单元格中的内容

C.单元格中的内容及其格式

D.单元格所在的行学