单项选择题
Most modern Loran-C receivers，when not tracking properly，have a（n）（）.
A.Bell alarm to warn the user B.Lighted alarm signal to warn the user C.Alternate signal keying system D.View finder for each station
单项选择题 Loran-C uses the multiple pulse system because（）.
单项选择题 Loran-C is which type of system（）.
单项选择题 In using Loran-C，skywave reception gives greater range but is（）.
