The centers are in big cities doesn't seem quite right. I don't event know what is meant by this. Are we talking about shopping malls? In that case I would say There are centers in the big cities or There are shopping malls in the big cities. Perhaps the meaning is The malls are in the big cities? I digress.
I wonder if maybe "center" here might mean "downtown area", like "centro" in Spanish?
Yes, "centru" means the centre of a village, town or city where many of the cultural/administrative buildings are located so it would be equivalent to a "downtown area."
Yes, marked wrong for "the centres are in large" "towns" Oras are towns in British English it would seem, and the hint offered both towns and cities.
Yes but looking at the context of the sentence, only cities are big enough to have 'centres'.
Unfortunately this sentence is not factual. In Romania, even "o comună" (i.e., a geographical/administrative gathering of several villages) usually has a a cultural/administrative centre where one can find at least one church, a community centre, an administrative building like "primăria" (a building where you can go talk to the mayor), a school, maybe a hospital or something along those lines to at least administer first aid ("infirmeria"), a store and a market (the latter might only be open on the weekend).
You will often hear people say "Mă duc în centru." (I'm going downtown.") or "Am fost in centru." ("I was downtown.")
I can only assume that the lesson is referring to a different type of "centre" that is only found in cities, like an central business district or similar.
Why isn't "towns" accepted here? Is there some way to distinguish when oras means city and when it means town?