Chandragupta's construction of roads and harbors most clearly demonstrated the importance of what aspect of governance?

The important aspect of governance is Public services. By building roads he showed how important it was for those who are in charge, in some cases monarchy in some cases parliament, to work for the well being of people through public services like building roads because then the local community can become better and richer too.

following type of cultural development caused people to want and buy new products on the market :

industrialization