What is the black plague ? and how did it start ? how was it being dealt with ? what area got hit the hardest ?

The Black Plague was the deadliest known pandemic. It resulted in the deaths of up to 75–200 million people. It was transmitted by fleas on rats to humans. They couldn't do much to stop it, and attempted to use unconventional methods to cure it. Central Asia or East Asia was where it originated, so that is probably the area that got hit the hardest.

answer; the intervening variable;

answer; /// decreasing responsiveness to a stimulus to which one is repeatedly exposed;