Rightward Demand Shift from Complement Price Change

Steps:

• A rightward demand curve shift means increased demand at every price, caused by non-price factors like related goods' prices.
• Complements are goods used together; a price drop in one boosts demand for the other.
• Substitutes compete; a price drop in one reduces demand for the alternative.
• The good's own price change causes movement along the curve, not a shift.

Why B is correct:

• A decrease in a complement good's price lowers the total cost of joint consumption, increasing demand for the original good per the law of demand for related goods.

Why the others are wrong:

• A: Decreased income reduces purchasing power for normal goods, shifting demand left.
• C: Decreased substitute price makes the alternative more attractive, shifting demand left.
• D: Decreased price of the good causes a movement down along the existing demand curve.

Final answer: B