Placer mining involves to extract minerals.
a. removing the top layer of earth
b. tunneling under the earth
c. dredging sediments from the water bottom
d. none of the above

Placer mining involves dredging sediments from the water bottom to extract minerals.  Correct C

This ancient method uses water to excavate, transport, concentrate, and recover heavy minerals from alluvial or placer deposits.

Typical minerals recovered in placers are minerals of high specific gravity and physical toughness, like gold, platinum, diamonds...

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