Dyst Tech made a proposal and statement of work for a website overhaul for the Town of Whitby in Ontario. Dyst Tech offered the municipality three different pricing structures. The lowest price option was available if a full lump sum was paid prior to the start of the project. The next price option was $15$ percent more than the first but allowed the municipality to pay in installments over the course of the project. The third price option was the most expensive, at $40$ percent more than the lowest price, with a requirement that payment be submitted within $60$ days of completion of the project. The lowest price option is what type of discount?

a$.$ functional discount

b$.$ seasonal discount

c$.$ cash discount

d$.$ quantity discount