He _____ in his English Test Paper. His teacher was very angry with him.       [ ]

A. makes some mistakes    

B. make a mistake

C. made few mistakes        

D. made many mistakes

（4分）电磁打点计时器工作电源是　　 （选填“直流”或“交流”）电源，电压为       V以下；电火花打点计时器是工作电压为          V，频率为50Hz时，每隔          s打一次点.