Lesson90TELEPHONES旧课件
日期：2010-07-01 07:02
Lesson90TELEPHONESLiYing1Whyweretelephonesnotpopularatthebeginning?2Whyweretelephonesexpensiveatthebeginning?3Whydidyouhavetowindthehandlebeforemakingacall?4Whatdidthetelephoneoperatordo?5Whatdoyoucallabookcontainingallthecustomers’telephonenumbers?PART36Whataresatellitesusedfor?7Whyarelightssignalsbetterthanelectricalsignals?，
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