Conjugate the verbs in the PRETERITE TENSE. Make sure you add accents if the conjugation needs it.
Nosotros (comenzar) con una excursión al Templo Mayor por la mañana.

I'm pretty sure it's

"Nosotros comenzamos con una excursion al Templo Mayor por la mañana."

English:

"Tomorrow we start with a excursion to the Templo Mayor in the morning"

Hope I helped ^.^

answer is a: las

explanation:

the reason for this answer is becouse it's a plural frase which talks more then one thing

same as the person below me