下列对多道程序设计的说法中；正确的是(20)。

(75)is　the　address　of　a　variable　or　a　variable　in　which　the　address　of　another　variable　is　stored.

The(74)has　several　major　components,　including　the　system　kernel,　a　memory　management　system,　the　file　system　manager,　device　drivers,　and　the　system　libraries.

One　use　of　networks　is　to　let　several　computers　share(71)such　as　file　systems,　printers,　and　tape　drives.

In　document　windows,　selected　text　is(70)

The　standard(68)in　C　language　contain　many　useful　functions　for　input　and　output　,string　handling　,mathematical　computations,　and　system　programming　tasks.

The　smallest　physical　units　on　a　hard　disk　are　called(69)

Note:　Make(67)regularly　in　data　processing.

If　your　diskette　has　been(66),　the　computer　can　not　store　any　new　information　on　it.

(46)

(45)