A-A+
The first electric lamp had two carbon rods fr
问题详情
The first electric lamp had two carbon rods from which vapor served to conduct the current across the gap.
A．The first
B．from which
C．served
D．across请帮忙给出正确答案和分析，谢谢！
参考答案
正确答案：B应改为bywhich。
解析：这里需要介词+关系词，按照语意，“在……周围，依赖……手段”用by。
