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When the object absorbs all colour frequencies

Explanation:

Certain materials absorb and reflect specific wavelengths of visible light, which results in objects taking on a certain color to the human eye. When nearly all light is reflected, you see white. When no light is reflected, you see black.

C

Explanation: Hope this help :D

It has crust and trough.

Explanation:

The oceans movements along the shore called waves because it has crust and trough just like waves and vibrates about its mean position. A crest is a higher point of wave whereas trough is the opposite of a crest and lowest point of a wave. Ocean waves is similar to sound and light waves because both waves travel as up and down vibrations and the energy present in these wave travels in forward direction.