"She was doing experiments but she did not understand the results!"
Translation:Ea făcea experimente, dar nu înțelegea rezultatele!
Why can I not say: Făcea experimente dar nu a înțeles rezultatele?
This seems to correspond to the English translation that Duo provides: "She was doing experiments but she did not understand the results!"
Is it because some verbs like "to understand / a înțelege" are only used in the imperfect tense and never in the "Perfect Compus" (i.e. passé composé)? (maybe this is the case with the verbs: to know, to see, to understand)
"Făcea experimente dar nu a înțeles rezultatele." should be accepted. Please report it.
In the Romanian translation, we can use both the perfect compus and the imperfect.
It is English where a number of verbs are not used in the continuous form ("-ing" ending), among them those mentioned by you. They are called Stative / Non-Continuous / Non-Progressive Verbs. More details on this: