Why are sub saharan rivers not very useful for travel

How many countries have portuguese as a national language?

:calculate the sum of the interior angles of a 13-sided polygon.

17. the soil erosion pictured here is the result of what? a. harvesting renewable resources at a rate greater than the sustainable yield b. a mudslide caused by excessive rains c. harvesting renewable resources at a rate lower than the sustainable yield d. the transition between geologic eras and eons