DL marked "Many new factories opened." as wrong, but in English this is equivalent to "Many new factories have opened." DL accepts "Many new factories are opened" which to me has a distinctly different meaning from "have opened" or "opened". I think the meaning of this sentence in Italian is ambiguous and can take on any of these English translations.
"Many new factories are open" was marked as correct for me.
According to Wordreference, AVERE is the auxiliary verb for APRIRE, so shouldn’t "Many new factories have opened" be translated as “Molte nuove fabbriche hanno aperto” and NOT “Molte nuove fabbriche sono aperte” as indicated as correct by DL. “Aperte” is an adjective and not part of a compound verb.
My thought is that "sono state aperte" would translate into English as "have been opened", i.e. the passive pluperfect form, which is logical as factories can't open themselves. Don't know if it helps but Google also uses this translation and also "are open" for the original sentence rather than the DL version. The more i think about it, the less correct the DL translation of "have opened" is sensible as again they don't open themselves. May be something to do with transitive and intransitive verbs which i have never understood in any language!