Which best describes a reason that consumer demand can change?

The correct answer is: "loss of income".

A demand function represents the quantity of a certain good or service that consumers are willing to purchase at different price levels. The income affects the amount that consumers are willing to buy because, if it decreases, so does the consumer's purchasing power and he will be able to buy fewer goods and services.

If the curve is represented in a graph, an income loss will generate a shift of the function to the left, as the picture attached shows. Both the equilibrium price and quantity will be reduced.