Back then, the answer would be A. But, if this was a MODERN question, the answer would be D.
Answer:Smallpox and vaccination are intimately connected. Edward Jenner developed the first vaccine to prevent smallpox infections, and this success led to the global eradication of smallpox and the development of many more life-saving vaccines.
Explanation:
The invention of the lightbulb allowed factories and mills to stay open longer and work through the night. Hope it helps :)