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The answer to this question would be: <span>lung cancer
In 1950, the medical practitioner doesn't know the relation of cigarette smoking with lung cancer. In that era smoking advertising is very massive and some physician even helps it. This cause increased amount of lung cancer incidence. The amount of lung cancer continues to increase till 1980-1990</span>
The solar system is considered a natural system because it was made and controlled by natural forces, meaning, it was never influenced with human creations. It is considered as one of the products of the phenomenon of the physical world. Hope this answer helps you.
I would go with the first option
