In using Loran-C，skywave reception gives greater range but is（）.

A.only accurate during daylight hours

B.much less accurate

C.only accurate at twilight

D.more accurate than using ground waves

防止间接电击的措施有（）。

A、绝缘

B、屏护

C、工作接地

D、保护接地

E、保护接零

F、保护开断