"Statele Unite ale Americii construiește multe avioane."
Translation:The United States of America builds many airplanes.
I am agreed with both of you, just I want to add that in another case, Duolingo used plural after SUA in a Romanian sentence. I will make and add when I spot it, because I do not remember it now. Maybe the "mistake" was made because the original sentence was in English and the translation was made automatically...