Final answer:
If a country's economy has begun to significantly expand and industries have started exporting to other countries, it is in the takeoff stage of economic development.
Step-by-step explanation:
If a certain country’s economy has begun to significantly expand and certain industries have begun to export to other countries, this country is in the takeoff stage of economic development. The takeoff stage is characterized by rapid growth and the emergence of export-oriented industries, which indicates that the country is transitioning from a less developed state to a more developed one. Examples of countries in this stage include South Korea, China, and other East Asian nations.