Zheng says that the most dangerous thing about a credit card is____ a person isn’t always aware of the fact____ he’s spending money.

A．that; that

B．what; that

C．that; what

D．what; which

晶闸管．直流电动机的调速系统属于（）。

A、调磁调速系统

B、变电阻调速系统

C、调压调速系统

D、调频调速系统