"Làm sao bạn biết cái liềm đó cổ?"

Translation: How do you know that sickle is ancient?

[Raphael_SyBo]

cái liềm sounds like "ký liềm" here

[TehVanarch]

In everyday speech the article "cái" is shortened to something like "cấ..." as in a short "cớ" or as you stated, a short "kí" sound.

[Raphael_SyBo]

Good to know, thank you ^^

[StewartMM]

How would you then say "How do you know that ancient sickle?" From what we have been taught, that would be the usual translation.

[vngdhuyen]

làm sao bạn biết cái liềm cổ đó?

the demonstrative determiner should be at the very end of a noun group. a short reminder:

quantifier + classifier + head noun + attribute + demonstrative determiner + possessive determiner