Demand shifters vs. supply shifters Steps:

• Recall that the demand curve shifts from changes in non-price factors like prices of related goods, income, tastes, or buyer numbers.
• The supply curve shifts from changes in production costs, technology, or seller numbers.
• Evaluate A: Lower complement price boosts demand for the product, shifting demand right.
• Evaluate B: Higher labor costs raise production expenses, shifting supply left but leaving demand unchanged.
• Evaluate C and D: Both involve related goods or alternatives, directly shifting demand. Why B is correct:
• Production cost changes (like labor) alter the supply curve per the law of supply, without impacting demand determinants or the demand curve's position. Why the others are wrong:
• A: Immediately shifts demand right as complements become cheaper, increasing joint consumption.
• C: Introduces more substitutes, shifting demand left as buyers have new options.
• D: Raises substitute price, shifting demand right as buyers switch to this product.

Final answer: B