signal for的用法和樣例：
例句
- The President's arrival was the signal for an outburst of cheering.
總統來到爆發一陣歡呼聲。 - I'll say `One, two, three, go!' as a signal for you to start.
我喊｀一、 二、 三、 開始!＇你就開始。 - The rise in prices was a signal for rebellion.
物價上漲引起了叛亂。 - A colored flare used as a warning signal for trucks and railroad trains.
信號火一種為卡車或火車作警告信號的有色火焰
