Answer:
The sentence: ¿___ Uds. las cebollas? is asking a group of people (Formal) if they completed a task (Cut the onions). Therefore, we use the preterite tense for this sentence to make:
¿Picaron Uds. las cebollas?¡ Las necesito ahora!
(Picaron is the ustedes conjugate for the preterite tense)
