在E-mailis atext-based message deliverysystem thatallowsinformationsuch astypedmessages and multimediatobe senttoindividual computerusers.整个句子中,E-mailis a system是句子...E-mail that must travel across town or across a country to reach the final destination usually travels throughthe telephone network. 这句中E-mail that must travel ··· destination是不是主语从句，帮我分析下谢谢你怎么把什么都当做主语从句啊。主语从句是作主语的“句子”，不是修饰主语的句子。这句话的基本结构是E-mail（主语） usually travels（谓语） throughthe telephone network（状语）. that（引导定语从句并在从句中作主语） must travel（谓语） across town or across a country to reach the final destination（状语）是修饰主语 E-mail的定语从句。如果觉得可以就采纳。