The first electric lamp had two carbon rods from which vapor served to conduct t

游客2025-05-04 5

问题 The first electric lamp had two carbon rods from which vapor served to conduct the current across the gap.

选项 A、The first
B、from which
C、served
D、across

答案 B应改为by which。

解析这里需要介词+关系词，按照语意，“在……周围，依赖……手段”用by。

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