PassageTwo
Questions26to30arebasedonthefollowingpassage.
Theelectr omagnetwasinventedinEnglandbyWilliamSturgeon，whotookanironrodandbentitintotheshapeofahorseshoe.This“horseshoe”wascoatedwithvarnishandalayerofcopperwirewaswrappedaroundit.Anelectr iccurrentwaspassedthroughthewire，thusmakingtherodmagnetic.Therodwasnow，becauseofmagneticattr action，abletosupportninepoundsofiron.IntheUS，ascientistnamedJosephHenryimprovedonSturgeon'selectr omagnetbyinsulatingthecopperwinewithsilk.Hewasabletowrapmanyturnsofwirearoundanironcorewithoutd angerofshortcircuitsbetweentheturns.Hismagnetcouldhold2,300pounds.ThisexperimentpromptedHenrytotr yhishandatconvertingmagnetismintoelectr icity.Firsthecoiledsomeinsulatedwirearoundanironbar.connectingbothendsofthewiretoagalvanometer(电流表).Theironbarwasplacedacrossthepolesoftheelectr omagnet.Thenthecoiloftheelectr omagnetwasconnectedtoabattery.Thegalvanometerindicatedavoltage，thendroppedtozero.Henrysignaledhisassistanttodisconnectthecoil.Thegalvanometershowedthatonceagainavoltagehadbeenproduced，althoughthistimeintheoppositedirection.Theprincipleofelectr omagneticinductionhadthusbeendiscovered.UnfortunatelyforJosephHenryhedidnotpublishhisfindingsandsomeoneelse(Faraday)gotthecreditforthediscovery.
Theprincipleofelectr omagneticwasdiscoveredby______.
A.WilliamSturgeon
B.JosephHenry
C.Faraday
D.someoneelse
正确答案：B[解析]答案见文章最后两句。
