How did the Hundred Years' War affect standing armies? It increased their power. It reduced their power. It gave their power to nobles. It gave them intermittent power.

The correct answer is that it increased their power

The standing armies were controlled by the kings and since the kings enjoyed the support of the people who started having nationalistic tendencies the support for standing armies grew as well. This was combined with the fact that nobles started losing influence and support which means that they wouldn't be able to have armies at their side and there would be a standing army of the entire nation.