A young river has very few tributaries and flows quickly. It's channels erode deeper rather than water. So, the answer is A.
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The ostrich runs 21 N then goes back by 25 S
The displacement is -4 S
21 - 25 = -4
Weathering of the rock and sedimentation are decomposition processes. Through time, the minerals in the rocks soften due to pressure and heat. So, they crumble down and reduce in terms of size. Once they do, they become sand or part of the soil. So, the answer is A.