【单选题】To make our school more beautiful, rubbish into the river.
【单选题】Trees and flowers _____ every year to make our school more beautiful. A. plant B. are planted C. were planted
【单选题】几位同学课后讨论直流电动机时,有下面几种说法,你认为不正确的是( )
B.
直流电动机的电源是直流电,线圈中的电流方向是不变的
C.
直流电动机中的换向器是由彼此绝缘的两个金属半环制成的
D.
直流电动机的优点是容易改变转动方向,可以连续调节转动速度
【判断题】直流电动机是将 机械能 转变 电 能 为的装置 。
【单选题】We must try our best to make our school more beautiful and ___ noisy.
【单选题】_______ has been done to make our school more beautiful.
【单选题】To make our school beautiful, we _____ throw rubbish here and there.
【多选题】关于直流电动机,下列叙述正确的是 [ ]
C.
直流电动机的换向器是由两个彼此绝缘的铜制半环组成的
D.
电源的正负极和磁场的方向同时改变,直流电动机的转动方向也改变