TGF11型四象限辅助变流器，采用（）变流技术。
A、交直
B、直交
C、交直交
D、直交直
参考答案：C
根据植物体的结构层次，填写下表。
—I came here by taxi and the driver ________ me 50 yuan.
—Really? You ________ by bus.
A．paid; should come
B．cost; should have come
C．charged; ought to have come
D．spent; ought to come
