The correct answer is: "commerce and taxes"
When a country has developed trade, it means that its production system is efficent enough to produce enough goods and services to satisfy the needs of its population, plus a production surplus which is sold through commercial activities. The more intense the trade activities conducted are, the more these would need to rely on more advanced technologies and on greater efficiency in the production process. Such situation brings sustained economic growth.
But many times, free markets do not conduct to a fair distribution of all the income generated by the production and trade activities. This is why advanced countries use taxation, collecting money to offer public services or aiding those in need.
