Concept:A change in demand means the whole demand curve shifts to a new position due to a non-price factor.
Explanation:Demand changes when factors other than the commodity's own price alter consumers' willingness to buy.
Such factors include income, tastes, expectations, and the availability of substitutes.
If close substitutes are available, consumers can easily switch between goods, so demand becomes more responsive and can change sharply.
The price of the commodity itself does not cause a change in demand; it only causes a movement along the same demand curve.
Supply of the commodity and technical know-how affect the supply side, not the demand side.
Therefore, among the options, the availability of substitutes is a correct factor affecting a change in demand.
Answer:B. Availability of the substitutes.