Final answer:
The conflict between Great Britain and China in the mid-19th century was primarily caused by British merchants selling illegal opium in China.
Step-by-step explanation:
The conflict between Great Britain and China in the mid-19th century was primarily caused by A. British merchants selling illegal opium in China. During this time, China imposed strict laws against the importation and distribution of opium, but British merchants smuggled it into the country, leading to addiction and social problems. The British government supported this illegal trade, which resulted in a military confrontation known as the First Opium War.
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