直流电动机（）时，把机械能转变为电能向电源回馈。
A.反接制动
B.能耗制动
C.回馈制动
D.倒拉制动
参考答案：C
I received a letter yesterday that my mother would come to our school.
A．said
B．says
C．saying
D．to say
STM-N信号的电接口码型为加扰的NRZ。（）
