Final answer:
A negative report on animal testing by the cosmetics brand would likely cause a leftward shift in demand, indicating a decrease in the quantity demanded at any given price and leading to a lower equilibrium price and quantity.
Step-by-step explanation:
The correct answer that would most likely cause a leftward shift in demand for a specific brand of cosmetics products is the one where journalists publish a sensational report in a major publication about the brand's secret history of testing its products on animals. This negative publicity can undermine consumer trust and preferences, thereby causing demand for the brand's cosmetics to decrease. The leftward shift indicates that at any given price, the quantity demanded of the cosmetics brand is lower than before, leading to a lower equilibrium price and quantity.
In contrast, options involving advertising success, celebrity endorsements, or price increases by the brand itself, typically suggest either a rightward shift in demand or movement along the demand curve, not a shift to the left. An increase in prices of its products might cause a movement up along the demand curve, leading to a decrease in quantity demanded, but not a shift in the demand curve itself.