Answer:
We must complete the sentence:
"Eduardo ____________________ dió una invitación a la fiesta a Mariana y Luis anoche."
It must be completed with a pronoun for Mariana and Luis, because they are two, we must use a plural pronoun.
One that fits the blank is "Les"
Eduardo Les dió una invitación a la fiesta a Mariana y Luis anoche.
Is the completed sentence.