功率三角形是指由电路的()组成的直角三角形。
A、电阻、电压、电流
B、有功功率、无功功率、功率因数
C、无功、功率因数、视在功率
D、有功、无功、视在功率
参考答案:D
_____ she couldn't understand was _____ fewer and fewer students showed interest in her lessons. [ ]
A. What; why
B. That; what
C. What; because
D. Why; that
铁路隧道与公路隧道通风和照明的比较?