Answer: A. Quand
Explanation: The first part is He will walk his dog.... he comes back from the office. Mais is but. But makes zero sense for this example. Car is because. Also makes zero sense. Parce que is because too. Quand means when. When makes the most sense
Bonsoir,
Nous allons à la boulangerie pour acheter du pain.
Aujourd'hui, nous sommes vendredi. Hope this helped you! <3