How did Andrew Carnegie use vertical integration to dominate the steel industry?

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. ... All these tactics made the Carnegie Steel Company a multi-million dollar corporation.

Explanation:

the answer is subjective. i personally agree with the first answer for this question.

if one isn't strictly talking about objects then the correct answer would be 'my eyes' since according to this riddle i am asleep and in order to answer/open the door i need to open my eyes first of all.

however, if one is specifically looking for an object, then the first thing i would open would be the door

hope this !