The chairman’s speech ______ the radio when I turned it on.A.was broadcast onB.was being broadcast onC.was broadcasting inD.broadcast over
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B解析考查时态以及介词的用法。从when I turned it on可知，前句应该用同进行时有关的时态；broadcast与speech之间存在被动关系，“通过收音机”可以用over/on the radio。“通过电视”则说：on TV（无冠词）,“通过报纸”through newspapers。