SoleAce, a luxury shoe$-$making company, intends to expand its sales in another country. However, it wants to do so with limited investment and risk. To this end, it partners with Comfies, an overseas premium socks manufacturing company. SoleAce and Comfies sign an agreement that allows each firm to sell the products of the other firm. As a result, both generate higher sales by promoting each other's products. Which of the following business forms has SoleAce adopted?

a$.$ Licensing

b$.$ Franchising

c$.$ Outsourcing

d$.$ Piggybacking