Answer: Use this link to find out the answer to your question - https://populationeducation.org/stage-1-demographic-transition-model/ (If you can't click it then just copy-paste it in a new tab)
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The answer is B. folding, uplift, and erosion. certain mountains are created from the folding of the upper layers of earth's crust. valleys on the other hand are made from the erosion of land or soil. tectonic uplift of the earths crust is also responsible for creating mountains.