I'd say the combustion engine, even though it was toyed with in the mid-west during the cowboy era, it wasn't until after the Civil War in which it was a fully effective gasoline powered engine.
Answer:
Some people believe it was man-made but there is no proof if it was or was not (i think it is man-made). It could be because the world is getting over-populated so this could be a way to wipe some people out.
The answer is A.
The Tokugawa Period (nicknamed "Edo") (1608 - 1868) was a period when Japanese society was under the rule of the Tokugawa shogunate, but has later brought internal peace to Japan for 250 years.