◎ 题干
They studied what ______ since 2007 and found Australian electricity prices were among the  highest in the developed world.
A.has happenedB.happenedC.had happenedD.has been happening
◎ 答案
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◎ 解析
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◎ 知识点
    根据n多题专家分析,试题“They studied what ______ since 2007 and found Australian electricity prices were among the highest in the developed world.A.has happenedB.happenedC.had happened…”主要考查了你对  【一般现在时】【将来进行时】【过去完成进行时】【过去将来时的被动语态】  等知识点的理解和应用能力。关于这些知识点的“档案”,你可以点击相应的链接进行查看和学习。