For this case we can translate the sentence given as:
The letters are ______________.
We must fill in the blank with the most appropriate option.
It is observed that the subject of the sentence is the "letters", in plural and feminine.
We must complete with a plural possessive pronoun including the first person, that is:
"Nuestras" The termination "as" is because the subject is feminine.
Answer:
Option A
La cartas son nuestras
