Which development occurred as the late 1800s?
part of the Second Industrial Revolution in the late 1800s?

A synergy between iron and steel, railroads and coal developed at the beginning of the Second Industrial Revolution. Railroads allowed cheap transportation of materials and products, which in turn led to cheap rails to build more roads. Railroads also benefited from cheap coal for their steam locomotives.

answer; i believe the correct answer is (favorable balance);

four sitting presidents have been assassinated while in office but the first was abraham lincoln,