The correct answer is A. Horizontal.
A horizontal demand curve is a curve that shows that the quantity demanded of a good or service does not change as the price of the good or service changes. This means that consumers are willing to buy the same amount of the good or service regardless of the price.
A vertical demand curve is a curve that shows that the quantity demanded of a good or service is zero at any price above a certain level. This means that consumers are not willing to buy any of the good or service at a price above that level.
A positively sloped demand curve is a curve that shows that the quantity demanded of a good or service increases as the price of the good or service decreases. This means that consumers are willing to buy more of the good or service at a lower price.
A negatively sloped demand curve is a curve that shows that the quantity demanded of a good or service decreases as the price of the good or service increases. This means that consumers are willing to buy less of the good or service at a higher price.
In the case of the question, the quantity demanded of the commodity remains unchanged regardless of changes in its price. This means that the demand curve for the commodity is horizontal.