That the application of new technology can increase the productivity of existing coal mines is demonstrated by the case of Tribnia’s coal industry.  Coal output per miner in Tribnia is double what it was five years ago, even though no new mines have opened.

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

1. If the number of miners working in Tribnian coal mines has remained constant in the past five years, Tribnia’s total coal production has doubled in that period of time.
2. Any individual Tribnian coal mine that achieved an increase in overall output in the past five years has also experienced an increase in output per miner.
3. If any new coal mines had opened in Tribnia in the past five years, then the increase in output per miner would have been even greater than it actually was.
4. If any individual Tribnian coal mine has not increased its output per miner in the past five years, then that mine’s overall output has declined or remained constant.
5. In Tribnia the cost of producing a given quantity of coal has declined over the past five years.                            

   答案是A，我觉得E也挺有道理，为什么E不对呢?人均产量提升，单位成本就下降了不是吗?

我看了象选C。原题说even though no new mines have opened, 都已经double了。

那加入开了新的，当然就更快了阿。

注意是per miner

如果有新的mine open,total output增加，但是per miner的productivity还是double.

we need to find the choice can be concluded from the statement.

但是D的描述建立在另一个假设上

并且就算“每个矿产量没有增加”这个假设成立，也未必能得出总产量减少，可能有新增煤矿来增加总产量。

understand?