What is adaptive radiation?
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a. a decrease in the rate of speciation
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b. an adaptation that harms an organism
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c. the process of learning new adaptations
d. when many species share a single ancestor

Adaptive radiation is the process of learning of new adaptations by the organisms and the plant.  

Explanation:

Adaptive radiations are the changes which are being adapted by the new generation of organisms for their survival. These adaptive radiations make difference between one generation and the other.

The common example of these changes are change in the thickness of beak of birds, changes of claws of birds, etc. Not only in organisms and animals, these changes are observed in plants also.

These changes are not inherited rather they are adapted according to the situation and nature.  

a. decomposes use carbon from dead organisms as fuel for cellular respiration, returning carbon dioxide back into the atmosphere.