Distinguishing movement along vs. shift in demand curve

Steps:

• Identify that movement along the demand curve (D) results from a change in the good's own price.
• Recognize shifts to D1 or D2 result from changes in non-price factors like income, tastes, or related goods prices.
• Evaluate each option: own-price change causes movement; others cause shifts.
• Select the option matching own-price change for movement along D.

Why B is correct:

• A fall in the price of good X, per the law of demand, increases quantity demanded, causing movement down along D.

Why the others are wrong:

• A: Advertising alters consumer preferences, shifting D right to D1 or D2.
• C: Fall in other goods' prices affects substitutes/complements, shifting D for X.
• D: Rising income changes purchasing power, shifting D (right for normal goods).

Final answer: B