What economic activity was profitable for spain and often the most hazardous for its workers?

The economic activity that was considered as profitable for Spain and sometimes or often the most hazardous or dangerous for the workers is mining. Spain has abundant reserves of uranium, lead, mercury, tungsten, fluorspar, magnesite, sepiolite, gypsum, nickel, iron, natural gas and crude oil. This is the reason why Spain is considered profitable when they include mining as their economic activity. However, the side effect of this activity is that it is not safe for those who are working in the mine.  

- tobacco.

- "rolfe reacted to consumer demand by importing seed from the west indies and cultivating the plant in the jamestown colony. those tobacco seeds became the seeds of a huge economic empire.the tobacco economy rapidly began to shape the society and development of the colony. growing tobacco takes its toil on the soil."

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answer; /// i believe that the correct answer is (d)the huang he river valley;