Treyvon is using the North American Industrial Classification System $($NAICS$)$ to research customers in his industry. He begins with the economic sector $"72$ Accommodation and Food Services." In order to get information on Hotels and Motels located in the United States, Mexico, and Canada, Treyvon should focus on $\_\_\_\_\_.$

a$.$ the five$-$digit industry group code $"72111$ Hotels $($except Casino Hotels$)$ and Motels"

b$.$ the four$-$digit industry group code $"7211$ Traveler Accommodation"

c$.$ the three$-$digit economic subsector $"721$ Accommodation"

d$.$ the six$-$digit U$.$S$.$ industry code $"721110$ Hotels $($except Casino Hotels$)$ and Motels"