The year gap of the population of 4 billion people was from 1974 - 1986. Exactly 12 years of 4 billion people.
The correct answer should be Adams' equity theory.
According to this theory, employees want to be equal at work, especially if they produce the same amount of work. So, if Bob and Tom do the same work, obviously they want to have equal paycheck as the other one, which is why Bob is unhappy because Tom's wage is higher.
Answer: When individuals and businesses are permitted to trade freely over a larger market area, they are able to produce a higher quantity of output and bring in different products.
Explanation: When businesses and individuals trade with one another, they are able to receive more items that they may not have been able to produce themselves. Trading freely allows for more people to have the opportunity to use other products that they can't make in their own country/state.
I'd say either railroads or wagon trains because airplanes and steamboats are not land travel and wagon trains are a vehicle and railroads are a thing they ride on to guide them
