OMS Corporation's top management has set a goal to increase the sales volume by $5\%$ at the end of the first business courter. To support this corporate$-$level goal, all departments in the organization are working hard to align their strategies with the goals. Which of the following statement is NOT the functional$-$level strategy?

a$.$ Purchasing department needs to purchase the expensive raw materials

b$.$ Marking department needs to advertise the company product to the public actively

c$.$ The HR department needs to hire additional employees

d$.$ The R& $D$ department needs to introduce new innovations and use technology to speed up the production process