In order to remain competitive, Big Bus Lines must reduce its average ticket price by 15%. However, the firm still wants to remain profitable. Which of the following options would allow Big Bus Lines to remain profitable while dropping its ticket prices?
A : decreasing its variable costs by at least 15%
B : increasing its variable cost per ticket by at least 15%
C : decreasing its number of passengers by at least 15%
D : decreasing its total fixed costs by at least 15%