Why isn't the non-American spelling of "litres" and "metres" accepted Duolingo!!??
Today (2017/03/05), they accepted "One litre has one thousand millilitres."
It's weird that sometimes they accept and sometimes they reject the spelling.
Each lesson has the list of possible answers manually maintained so they often don't line up. Using the report button helps them to improve things.
Do Romanians actually say that one litre has 1000 millilitres? While I'm asking, do English-speaking people say that? I would say one litre is 1000 ml.