Certain elements, such as carbon and nitrogen, are recycled in nature and are released through the of living things.
a.) metabolism
b.) decomposition

Decomposition

Explanation:

According to the carbon cycle when organisms die they decompose and release carbon.

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The right answer is B) decomposition

Explanation:

Elements like carbon and nitrogen are major constituents of living structures (cell membarnes, proteins, carbohidrates, etc). These elements are incorporated in living structures through metabolism. Structures containing carbon and nitrogen can enter soil from excretes, dead matter and other sources and will experience a process called decomposition, by which microorganisms reduce structures in its components (carbon and nitrogen for expample) and released them.  

his research revealed two genetically different groups of prokaryotes, which justified splitting kingdom monera into two kingdoms. the genetic and cellular differences were so great, that these two kingdoms were eventually placed into different domains in the current three-domain system.