The answer is <span>b. water erosion
Water erosion moves water downhill and during this process, different landforms are formed. <u>Some of them are rills, gullies, streams, rivers, tributaries</u>, waterfalls, floodplains, meander, lakes, etc.</span>
Rainwater is the main solution. There would need to be higher technology, to make that happen.
Plains have a higher population density because plains are easy to reach and at plains people get a number of resources necessary for their survival and livelihood.
The Glossopteridales is the correct answer
