某交流的电压随时间变化的规律如图所示，则此交流电的频率为______，若将该电压加在一阻值为1kΩ的纯电阻用电器，用电器恰能正常工作，则该用电器的额定功率为______．

Whose duty is it to examine and verify the vessel’s classification and technical state and condition?（）.

A.Tallyman's

B.Marine surveyor's

C.Cargo surveyor's

D.Boarding inspector's