(The first) electric lamp had two carbon rods (from which) vapor (served) to con

游客2025-05-04 6

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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(Thefirst)electriclamphadtwocarbonrods(fromwhich)vapor(served)tocon