第15题:[单选题]电动机的旋转磁场的转速与( )有关 A.电源电压成正比 B.电源的频率和磁极对数成正比 C. 电源频率成反比,与磁极对数成正比 D. 电源频率成正比,与磁极对数成反比 参考答案:D
第16题: [单项选择]In rough weather,when a ship is able to maneuver,it is best to launch a lifeboat(). A. on the lee side B. on the windward side C. with the wind dead ahead D. with the wind from astern 参考答案:A