These are the choices I found on the internet:
a. product differentiation.
b. price discrimination.
c. the level of the concentration ratio.
d. the number of firms in the industry.
e. whether they produce industrial or consumer products.
The answer would be letter B - price discrimination. Since a price maker is an entity/firm, with a monopoly that grants it the ability to affect the price it charges as the good it produces does not have perfect substitutes.