A、have reserves of power B、have other electric reserves C、ensure the steady flow of electricity D、ensure the operation of genera

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问题

选项 A、have reserves of power
B、have other electric reserves
C、ensure the steady flow of electricity
D、ensure the operation of generators

答案B

解析从原文该句可以知道为了维持60赫兹的交流电频率，PJM Interconnection必须have other electrical reserves，因此，本题应选B。

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大学英语六级

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