题目

小明观察了市场上的测重仪后，设计了如图5四个电路（R是定值电阻，R1是滑动变阻器）．可以测量人体重的电路是（      ） 答案：  A—I don't think we have met before.—Yes, once at a party, but we________．A.weren't introducedB.didn't introduceC.haven't introducedD.were not introducing