Based on the facts provided about the region, a reasonable inference would be:
4. Air and water pollution are probably major environmental problems in the region.
This inference is supported by the high percentage of the population living in cities with coal-burning factories, which typically contributes to significant air and water pollution issues. The other options do not necessarily align with the information presented. For example, while agriculture may be present, it's not indicated as a major economic activity, and the level of education does not directly imply an aging population or widespread poverty.