Actually, just two letters will do: delta and eta.

事实上，只须两个字母就已经足够：delta和eta。

youdao

For example, creating alias ll 'ls -hlt' reduces a commonly used command line to just two letters-less to type and less to remember.

例如，命令alias ll ' ls - hlt '将一个常用的命令行缩减为两个字母，从而使要输入和要记住的东西变得更少。

youdao

The bunny letters started arriving just two days ago. I've already received 30.

两天前我开始陆续收到关于兔子的信件，到目前为止已经有三十封了。

youdao

Can you clarify -- is that three facilities and letters total, or just two?

WHITEHOUSE: Press Briefing

It can read 10 million letters of genetic code, with a high degree of accuracy, in just two hours.

FORBES: Magazine Article