gǔ / rén / cháng / yòng / jiǎ / yǐ / bǐng / dīng / lái / biǎo / shì / shùn / xù

古人常用甲乙丙丁来表示顺序。

In ancient times, people often used jiǎ, yǐ, bǐng, and dīng to indicate order.