Final answer:
An increase in the price of imported resources would raise production costs, leading to a reduced quantity supplied at any given price and shifting the aggregate supply curve to the left.
Step-by-step explanation:
The factor that would increase per unit production cost and therefore shift the aggregate supply curve to the left is 'C) an increase in the price of imported resources'. An increase in the price of imported resources raises the costs of production for firms that rely on these resources, leading to lower profits at any given selling price. Consequently, firms would supply a smaller quantity at any given price, resulting in a leftward shift of the supply curve.