The first signal did not include the color yellow for caution, but that was later added within a few years.
第一次信号中不包括用于“注意”的黄色，黄色是以后几年内后加的。
The first trial in the 1830s, that of choosing green for the caution signal, and clear for the go signal, failed miserably.
第一次试验是在十九世纪的三十年代。起初他们选择绿色作为“注意”信号，明亮作为通行的信号，结果遭到惨败。
The first trial in the 1830s, that of choosing green for the caution signal, and clear for the go signal, failed miserably.
第一次试验是在十九世纪的三十年代。起初他们选择绿色作为“注意”信号，明亮作为通行的信号，结果遭到惨败。
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