impossible things to happen; something that will never come true; an utterly impossible event
要想让他放弃这个机会，简直是马角乌白，他早就下定决心了
To make him give up this opportunity is as impossible as horses growing horns and crows turning white; he has already made up his mind.
Era:
Ancient
Frequency:
Story:
During the late Warring States period, the Qin and Yan states maintained a superficial peace, exchanging royal princes as hostages.
Crown Prince Dan of Yan was held hostage in Qin, where King Ying Zheng treated him with extreme rudeness and disdain.
Prince Dan pleaded with the King of Qin for permission to return to Yan, but the King replied that he would only allow it if horses grew horns and crows turned white.
Prince Dan eventually escaped back to Yan and dispatched Jing Ke to assassinate the King of Qin.
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