"The religion of the Greeks was paganism."
Translation:Religia grecilor a fost păgânismul.
”Era” is also acceptable, since the English phrase gives no insight as to whether it ever stopped being (paganism). Since the imperfect is used when an action is in the past but does not have a defined end point (like past continuous in English), it most certainly can be translated as imperfect. The counterargument could be made that the Greeks dont practice paganism anymore and that this factor is implied in the past perfect definition that DL sticks to, but even in this case, from a morphosyntactic viewpoint there is no reason why the imperfect could not be used - and, the more I think of it, should not be used - in place of the given past perfect solution.
Well it's kind of a nuance thing. "A fost" is compound perfect, which is more often used in order to reffer to an event which is more distant in time, while "era" is imperfect( actual name of the tense) which reffers to an event closer in time to the moment of speaking. (There is a whoke axis for this if you want to look it up)
Perhaps you are right about the nuance thing, but you are not correct about the second part - imperfect has no relation to the time distance from the moment of speaking. The imperfect tense definition goes like this: "Verbal tense from the indicative mood group denoting a past action not finalized at the moment that we refer to" So please, try not giving erroneous definitions.