A black flag in a car race is the signal for a driver to go to the pits.

在汽车比赛中，黑旗是要车手进维修站的信号。

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The intervention would send a "chilling signal to all voters, but especially African Americans," said Mr. Steele, who is black.

按照Steele先生的说法，这种介入会给所有的投票人发出残酷的信号，尤其是非洲裔美国人，他本人也是个黑人。

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The last message from the pilot was a manual signal at 11pm local time, in which he said he was flying through an area of black, electrically charged clouds with violent winds and lightning.

在当地时间11pm，飞行员发出了最后的信息，这条信息是手动发出的，声称他们正在飞越一个有着暴风和闪电的带电黑云。

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How could I signal to potential allies across the vast black reaches of interpersonal space?

NEWYORKER: Raj, Bohemian

For the first time, scientists have detected an oscillating signal of a star being destroyed by a supermassive black hole.

FORBES: Scientists Detect Star Being Devoured By Supermassive Black Hole

There, among 12-foot high stacks of old oscilloscopes and signal-conditioning gear, Williams points to a clunky black metal box about the size of an underwear drawer.

FORBES: Magazine Article