What vegetation is commonly found in the flat low-lying areas ?

Floodplain forest is a bottomland, deciduous or deciduous-conifer forest community occupying low-lying areas adjacent to streams and rivers of third order or greater, and subject to periodic over-the-bank flooding and cycles of erosion and deposition.

Explanation:

Grasslands are, as their name suggests, flat and open areas where grasses are the dominant type of vegetation. Grasslands can be found on every continent except Antarctica.

c. bounced back and forth from worthless to worth a lot and back to worthless

the term is einsatzgruppen