单项选择题
A.Card B.Needle C.Lubber's line D.Gimbals
A.on loran charts covering areas where sky waves are used B.in the Radio Aids to Navigation,PUB 117 C.in the Loran-C Correction Tables D.Sky waves cannot be matched to ground waves in LORAN-C to produce a usable reading
A.full confirmation B.precise appreciation C.immediate assessment D.timely recognition