Final answer:
The Allies faced a severe food shortage in September of 1915, exacerbated by the British blockade, leading to rationing and unrest among the civilian populations in Germany and Austria-Hungary. The correct option is B.
Step-by-step explanation:
The potentially dire situation the Allies were facing in September of 1915 was a food shortage. In Germany, for instance, despite soldiers being prioritized in the food supply chain, the British blockade drastically reduced the availability of food, leading to bread rationing and a severe shortage in the winter of 1916-1917, resulting in a reliance on turnips as a food source.
Similar issues arose in Austria-Hungary which, lacking Germany's infrastructure, struggled even more with feeding its civilian population. The food shortages were severe enough to cause unrest and question the governments' war efforts, significantly affecting morale.