The answer is C. subjecting the president to checks by Congress.
Plessy<span> v. Ferguson, 163 US 537 (1896) was a landmark </span>constitutional<span> law case of the US </span>Supreme Court<span> decided in 1896. It upheld state racial segregation laws for public facilities under the doctrine of "</span>separate but equal<span>"</span>
This is a process known as horizontal integration. Carnegie also created a vertical combination, an idea first implemented by Gustavus Swift. He bought railroad companies and iron mines. If he owned the rails and the mines, he could reduce his costs and produce cheaper steel.