The correct answer is Intrastate
Step-by-step explanation:
If the buses of a specific company never leave the state this means the company only works inside one specific state. In this context, the best word to describe this company is "intrastate" which means "within the state" because all the lines of this bus company are inside or within the state. In the same way, adding a different prefix would change the meaning for example if the word "interstate" is used, this suggests the buses travel between two or more different states.