Answer:
A. They limit human work in hazardous enviroments.
Explanation:
Answer: diseases
Measles and Black Death/Bubonic Plague were both diseases, and they were very common among Medieval Europeans. The answer to the question is diseases.
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For years, China had enjoyed a favorable balance of trade with foreign nations. But the British trade of Opium with China disrupted the economy in the early 1800s and led to wars between the two nations.
The illegal trade of Opium that Britain was having with China caused a deep disruption of society and economy, leading to the First and Second Opium Wars.
Most African-Americans in the united states found themselves increasingly left out of the political process because of poll taxes and literacy tests.