Final answer:
The preterite form of the verb 'salir' for the subject 'ellos' is 'salieron'.
Step-by-step explanation:
The correct answer is a. salieron. The preterite form of the verb 'salir' (to go out) for the subject 'ellos' (they) is 'salieron'. Therefore, the sentence should be 'Al final, ellos salieron a comer almuerzo en el restaurante'.
Learn more about Verb conjugation in Spanish