Read the thesis statement from an argumentative essay about the importance of National Parks to the economy. National parks are very influential role in the economy of the United States because they encourage tourism and create job opportunities. Which statement could the essay's writer use to support the central claim made here?

Consider the following invention from the american industrial era. cotton gin – a machine that removed seeds from short-staple cotton which option explains how this invention contributed to the role of the united states as an emerging world power? a. it was in high demand abroad, as many european nations had begun farming cotton. b. it led to the decline of slavery in the south, which enhanced america’s international reputation. c. it freed up many slaves to become factory workers in northern cities, which improved the economy. d. it increased production efficiency of a us cash crop that was in high demand in other nations.