The answer is D. Nighttime
Answer: Both smallpox and COV 19 are novel diseases in their respective timelines. Both spread by inhaling infected droplets, albeit COV 19 is transmitted through aerosols and surfaces touched by infected people as well.
Explanation:
it's very practical, because it's on base 10, so conversion between stuff like meters to kilometer is always just a multiplication with 10 to some power
like 1 km = 1000m (10³m)
or 1 m = 10^-3km = 0.001km
same reason for other SI units.
except time, that's base 60, or 12, or 24. that's more complicated, but there isn't any real competition