"Where did you all eat last Friday?"
Translation:¿Dónde comieron ustedes el viernes pasado?
Why can't the answer be worded as "¿Dónde ustedes comieron el viernes pasado?
Because subjects (in this case, «ustedes») can't be used exactly after a question word (in this case, «dónde»). Although after a «por qué» might still be accepted.
Why do you use ustedes here? And why is it comieron - not comisteis? I'd think it was comisteis, when it's not "they" I am talking to, but "you" in plural.
For the record, I wrote "Dondé comisteis el viernes pasado" and got it wrong.
I wrote "dónde comieron el viernes pasado" and also got it wrong. I wonder if it is requiring the pronoun... would it accept "dónde comisteis vosotros el viernes pasado"?
ETA: yes, it did accept "dónde comisteis vosotros el viernes pasado". So I wonder why the pronoun is required ???!