加入钒钛矿对于炼铁生产（）有利。
A、洗炉
B、护炉
C、增铁
参考答案：B
I really appreciate for your introduction; actually we ____ each other before.
A have met B had met C met D meet
If the DSC controller is configured for MF/HF operation, the distress will be sent on（）.
A.double frequencies
B.single frequency
C.dedicated frequency
D.multiple frequencies
