Which of the following statements describes why the central lowland region is primarily tall-grassland prairies?

a) recurrent natural fires prevented trees from growing.
b) generally, there is insufficient rainfall to support trees.
c) cold air masses continually descend from the north.
d) only grass can grow on the marshy lands.

a) Recurrent natural fires prevented trees from growing.

Humid continental climate is found in the interior of continents between the 30 and 60 degrees latitude, but usually above the 40 degree line.   40 degrees north of the equator means less direct sunlight and therefore less warmth.   this climate is mainly found in the northern hemisphere since there are no major landmasses in the southern hemisphere.  if you live in northern indiana, you know all about humid continental because that is the climate type you have!