隐形墨水已经有一段历史了。

INVISIBLE ink has a lengthy history.

youdao

声明中相关部分必须用隐形墨水书写。

the relevant part of the statement must be written in invisible ink.

youdao

想，想，想，想，隐形墨水！

Think, think, think, think, invisible ink!

youdao

要怎样才知道什么时候隐形墨水用完了？

How do you tell when you run out of invisible ink?

youdao

要怎样才知道什么时候隐形墨水用完了？

How do you tell when you run out of invisible ink?

youdao