什么叫正弦电流？
参考答案：
正弦电流指随时间按正弦规律变化的交流电流。
I can’t remember _____ made the teacher give Mary the permission to leave the class earlier.
A．that it was what
B．what it was that
C．what was it that
D．that was it what
家庭氧疗的动脉血气指征是（）
A.PaO2<50mmHg
B.PaO2<60mmHg
C.PaO2<55mmHg
D.PaO2<70mmHg
E.PaO2<80mmHg
