Combined Shifts in Demand and Supply Steps:

• A fall in demand shifts the demand curve leftward, reducing equilibrium price and quantity.
• A decrease in production costs shifts the supply curve rightward, reducing equilibrium price and increasing quantity.
• The price effect reinforces: both shifts lower price, so price decreases unambiguously.
• The quantity effect opposes: demand fall lowers quantity, supply increase raises it, so quantity is indeterminate.

Why A is correct:

• Reinforcing downward pressure on price from both shifts ensures price falls, while opposing quantity effects make the change uncertain, per supply-demand equilibrium analysis.

Why the others are wrong:

• B: Price decreases definitively, not uncertain.
• C: Price decreases definitively, not uncertain.
• D: Price decreases definitively, not uncertain.

Final answer: A