Option B: this could not work. The underlined word is a personal pronoun, but it has a stated antedecent: Jacob, which is a vocative separated by a comma.
Option C: does not work. Carla said (that) she was leaving... "she" is preceded by a reported speech; a reporting verb: say.
Option D: this possesive pronoun "our" is preceded by more information.
Therefore, option A is the best one. "We" is suject the of the sentence, and it does not have anything written before it.
