Dams are costly, but once they have been built, ______electricity very cheaply.A

游客2025-02-04 18

问题 Dams are costly, but once they have been built, ______electricity very cheaply.

选项 A、producing
B、they produce
C、production of
D、and produce

答案 B

解析 The third clause needs a subject and a verb: they produce.

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Damsarecostly,butoncetheyhavebeenbuilt,______electricityverycheaply.A