DF4B型内燃机车硅整流装置每一桥臂上由（）整流元件并联而成。
A、4个
B、6个
C、8个
D、7个
参考答案：B
—Is chemistry more difficult than physics?
— No, chemistry isn't as _____ as physics. [ ]
A. easy
B. difficult
C. easier
D. more difficult
咨询服务采购、竞争和评审以( )为主。
A．技术 B．价格C．服务 D．质量
