A.一短聲 B.二短聲 C.三短聲 D.四短聲
A.L≥100m B.20m>L≥12m C.100m>L≥20m D.L<12m
A.手搖鈴號笛、號鐘和手搖鈴 B.號笛、霧角和號鑼 C.號笛、號鐘和霧角 D.號笛、號鐘和號鑼