进入煤气区域抢救人员必须佩戴（）或（）。
参考答案：空气呼吸器；氧气呼吸器
He was satisfied because his work was_________.
A．high thought
B．high thought of
C．good thought
D．well thought of
A．变压器输出端所接电压表的示数为20V
B．变压器的输出功率为200W
C．变压器输出端的交流电的频率为50Hz
D．穿过变压器铁芯的磁通量变化率的最大值为20/n2Wb/s
V
/n2Wb/s