A manager at JCPenney discovers that Dillard's has reduced the price of its children's Levi's from $$31\mathrm{.}99$ to $$24\mathrm{.}99,$ according to an advertisement in the Sunday newspaper. She immediately phones her store and instructs the salesperson on duty to put a sign up next to their children's Levi's that reads, "SALE: $$24\mathrm{.}99."$ This is an example of what pricing strategy?

a$.$ Comparison discounting

b$.$ Secondary$-$market pricing

c$.$ Reference pricing

d$.$ Random discounting

e$.$ Periodic discounting