I think that the poster in question has the title of "plant a victory garden" and a further comment of "A Garden will make your rations go further".
This poster motivates people to find food in their own gardens and links this to the war efford, so the best answer is that:
D) Peoples' actions on the homefront were vital to winning the war
(if people back home made food for themselves, more food could go to the soldiers).
