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The Call of Duty 4 campaign is strictly single player.
Yes
complete the campaign
In Call of Duty: Black Ops, to go on multiplayer you have to go to multiplayer on the menu that says: CAMPAIGN MULTIPLAYER ZOMBIES OPTIONS
There are several ways to play call of duty, if you have a device that does not connect to the internet then there are single player options. Also there is a campaign option which is single player and you do not need to be connected to internet.