Answer:
The costs of passing a bill that prohibits child labor is precisely that all the labor that children could have provided for the economy is forgone. So in pure economic terms, there is a loss of value, a sunk cost.
However, the benefit is both economic, and social. The economic benefit is that children will instead go to school, and educate themselves to become more productive workers in the future. And the social benefit is a fairer society, and wealthier too.
I believe the answer is A. Production increased due to the demand for goods worldwide.
It is false that Communism was the dominant economic force of the twentieth century, although it certainly overtook a great deal of territory. Capitalism was still overall dominant.