Iron ore mines in Triberia have demonstrated that upgraded

Iron ore mines in Triberia have demonstrated that upgraded technology can result in large increases in productivity level. In a country where no new iron ore mines have been opened, Triberia's iron ore output per miner has doubled during the last 5 years.

Which of the following can be properly concluded from the statement about iron ore output per miner in the passage?

(A) If any new iron ore mines had opened in Triberia in the past five years, then the increase in output per miner would have been even greater than it actually was.

(B) In Triberia the cost of producing a given quantity of iron ore has declined over the past five years.

(C) Any individual Triberian iron ore mine that achieved an increase in overall output in the past five years has also experienced an increase in output per miner.

(D) If any individual Triberian iron ore mine has not increased its output per miner in the past five years, then that mine's overall output has declined or remained constant.

(E) If the number of miners working in Triberia iron ore mines has remained constant in the past five years, Triberia's total iron ore production has doubled in that period of time.

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