"Liters are units" or "A liter is a unit" or "The liter is a unit." People in the UK and Canada may also spell it "litres."
Terima kasih, Pak James.
Your suggestions are added to the list of acceptable answers.
Please don't forget to submit a report the next time you see an incorrect/awkward translation.
I didn't think this one was worth it, but for a lot of these sentences, the option "The English sentence is wrong or unnatural" is not offered. It would probably streamline the process if that option could be added.