填空题 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


  • 1、
【正确答案】 1、B应改为by which。    
【答案解析】[解析] 这里需要介词+关系词，按照语意，“在……周围，依赖……手段”用by。