The 350km/h EMU is composed of four power distributed cars. It adopts the electric traction AC (alternative current) transmission way, which includes two _____________, and each unit is composed of two motor cars and one trailer car. 350公里/小时动车组由4辆动力分散车辆组成。 采用电动牵引交流传动方式，它包括两个__________，每个单元由两辆动力车厢和一辆拖车组成。
A、traction car 牵引车厢
B、traction unit 牵引单元
C、locomotives 机车