A real estate firm has three offices. Which of the following statements BEST describes its obligation to display the firm's license certificate$($s$)?$

A$.$ The license certificate must be prominently displayed at the main office only.

B$.$ The license certificate must be displayed at the main office with copies posted at each branch.

C$.$ The license certificate must be displayed at the main office with the license of the supervising broker displayed at each branch office.

D$.$ A license certificate must be obtained for and displayed at each office.