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单选题（） is a protocol for mail services.
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单选题 （） is a protocol for accessing and transferring documents on the WWW.
填空题 A ____is a set of rules that controls the interaction of different devices in a network or internetwork.
填空题 The ____model is a theoretical model that shows how many two different systems can communication with each other.
填空题 The seven layers of the OSI model are the ____layer, ____layer, ____layer, ____layer, ____layer, ____layer, and____layer.
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