Which type of primary research typically requires no direct involvement with human subject?

Which of the following statements best describes the terms of the treaty of guadalupe-hidalgo? a the treaty ended the mexican-american war, resulting in the u.s. finally being able to finish building railroads in texas. b the treaty ended the mexican-american war, resulting in mexico and the u.s. going back to their pre-war conditions. c the treaty ended the mexican-american war, resulting in the u.s. facing a lot of international backlash for the war. d this treaty ended the mexican-american war, resulting in mexico ceding a large amount of land to the united states.