The Kimmy J Social Beauty Company is struggling to meet its marketing objective despite the strong social media presence of its founder. To determine why the firm is failing to reach its performance targets, the company's executives are conducting a cost analysis in the hopes of identifying ways to reduce costs so that they can lower prices and promote the greater value of their products. Which of the following is NOT a fixed cost that is easily lowered?

a$.$ Employees' salaries

b$.$ Selling costs

c$.$ Commissions

d$.$ Shipping costs

e$.$ Material costs