A shift in a demand curve occurs due to:

A shift in the demand curve is primarily caused by changes in factors other than the price of the good itself. These factors can include changes in consumer income, preferences, the prices of related goods (substitutes and complements), demographic shifts, and consumer expectations about future prices. When any of these factors change, they affect the overall demand for a product at all price levels, resulting in the entire demand curve shifting to the left (decrease in demand) or to the right (increase in demand).

In contrast, adjustments in the price of the good itself result in a movement along the demand curve rather than a shift. Similarly, changes in supply, government policies, or other external factors may influence market dynamics but do not shift the demand curve directly. Understanding this distinction helps clarify why option B accurately describes the reasons behind a demand curve shift.