The Demand Curve for a Good Is Very Unlikely to Be

Multiple Choice

The demand curve for a good is very unlikely to be perfectly vertical because

A) scarcity and limited income restrict the ability of consumers to afford goods as they become very expensive.
B) as the price of a good rises to high enough levels, the incentive for other suppliers to invent new substitutes for the good increases.
C) consumers generally do not care about the price of the goods they consume.
D) both a and b are true.