甲乙丙丁 A, B, C, D
Explanation
天干的最初四个字，顺序为甲、乙、丙、丁。也用来泛指事物的顺序或大概轮廓。
The first four characters of the Heavenly Stems, in order: Jia, Yi, Bing, Ding. Also used to generally refer to the order or general outline of things.
Origin Story
话说唐朝时期，长安城里有一家茶馆，生意特别好。茶馆老板姓李，他请了四个伙计帮忙，分别叫做甲、乙、丙、丁。甲最勤快，总是第一个到茶馆，负责打扫卫生和准备茶具；乙擅长泡茶，泡出的茶香气四溢，深受顾客喜爱；丙负责记账，他的字迹工整，账目清晰；丁则负责招待客人，他为人热情，总是面带微笑。这四个伙计各司其职，配合默契，茶馆的生意越来越红火。有一天，一个顾客问李老板：“你们这四个伙计，谁最厉害？”李老板笑着说：“他们各有各的长处，没有谁最厉害，只有最合适的。甲乙丙丁，如同天干一样，缺一不可。”
During the Tang Dynasty, there was a teahouse in Chang'an city that did exceptionally well. The owner, whose surname was Li, hired four assistants named A, B, C, and D. A was the most diligent, always arriving first to clean and prepare the tea set; B excelled at brewing tea, his tea fragrant and highly favored by customers; C was responsible for accounting, his handwriting neat and accounts clear; D was in charge of greeting guests, always enthusiastic and smiling. Each assistant performed their duties expertly, and the teahouse thrived. One day, a customer asked Mr. Li, “Which of your four assistants is the best?” Mr. Li replied with a smile, “They all have their strengths, none is the best, only the most suitable. A, B, C, and D, like the Heavenly Stems, are all indispensable.”
Usage
常用来表示事物的顺序或轮廓，也指大致的类别。
Often used to indicate the order or outline of things, but also for rough categories.
Examples
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甲乙丙丁四个同学一起合作完成这个项目。
jiǎ yǐ bǐng dīng sì ge tóngxué yīqǐ hézuò wánchéng zhège xiàngmù。
Four students, A, B, C, and D, worked together to complete this project.
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公司根据甲乙丙丁四个等级对员工进行考核。
gōngsī gēnjù jiǎ yǐ bǐng dīng sì ge děngjí duì yuángōng jìnxíng kǎohé。
The company evaluates employees according to four levels: A, B, C, and D.
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这几个方案，我只能说个甲乙丙丁，具体哪个好，还要再研究。
zhè jǐ ge fāng'àn，wǒ zhǐ néng shuō ge jiǎ yǐ bǐng dīng，jùtǐ nǎ ge hǎo，hái yào zài yánjiū。
For these options, I can only say which are A, B, C, and D. Which one is better needs further study.