A)for several thousand years.
B)since the middle ages.
C)since the late 1800s.
D)since the 1950s.

A)that is due to a greater degree of interaction between humans and tick-carrying animals.
B)that is due to a decline in vaccinations.
C)that is due to a mutation in the human genome.
D)that is due to climate change leading to a greater mosquito population.

A)occurred during the late 1800s to early 1900s.
B)started in the 1990s with the advent of genetic engineering.
C)is a time when the knowledge of and techniques to work with bacteria blossomed.
D)was when people realized that diseases could be caused by invisible agents.
E)occurred during the late 1800s to early 1900s, is a time when the knowledge of and techniques to work with bacteria blossomed AND was when people realized that diseases could be caused by invisible agents.