It was only after some progress______ in the use and development of electric current that men began to realize the importance an

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问题 It was only after some progress______ in the use and development of electric current that men began to realize the importance and possibilities of magnetism.

选项 A、was made
B、would have been made
C、has been made
D、had been made

答案D

解析 分析题干可知,本题陈述的是发生在过去的事实,而非虚拟,故排除[B]。由only after…that…“只有…之后,才…”可知,电流的使用和发展上的进步发生在人们意识到磁场的重要性之前,即前一个动作完成之后才会有后一个动作,因而填空处需要使用过去完成时,故答案为[D]。
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