What responsibilities does the United States have as a world leader?

The President is responsible for implementing and enforcing the laws written by Congress and, to that end, appoints the heads of the federal agencies, including the Cabinet. ... The Cabinet and independent federal agencies are responsible for the day-to-day enforcement and administration of federal laws.

a historian researching the immigration policies of the early 1900s would expect a source written today,rather than in 1910 to :

( a ) be more interested in objective data and statistics.

i think it's a)sparta