单选题On navigational aids，what does the light characteristic Fl(2+1) mean?（）AA flashing light combined with a fixed light of greater brightnessBLight flashes combined in groups，with a different number of flashes in each groupCA light showing groups of two or more flashes at regular intervalsDA fixed light varied at regular intervals by groups of two or more flashes of greater brightness
单选题
On navigational aids，what does the light characteristic Fl(2+1) mean?（）
A
A flashing light combined with a fixed light of greater brightness
B
Light flashes combined in groups，with a different number of flashes in each group
C
A light showing groups of two or more flashes at regular intervals
D
A fixed light varied at regular intervals by groups of two or more flashes of greater brightness
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