The variable regions of the heavy and light chains form the sites of an antibody.

Antigen binding fragments

Explanation:

Antigen binding fragments are site locations that promote antigen-antibody binding, promoting complete protection of the organism. These fragments have specific molecules between antibody and antigen, so we can say that through the antigen binding fragments each antibody is antigen specific. In summary, we can state that the variable regions of the heavy and light chains form the antigen binding fragments sites of an antibody.

there are mainly three domains in biological classification namely; archaea, bacteria, and eukarya.

archaea includes all the prokaryotic cells which are characterized by their lipid membranes. they have branched hydrocarbon which is attached to glycerol through an ether linkage.

bacteria includes all the prokaryotic cells, the cell membrane of which are made up of the unbranched fatty acid chain. in addition, they are attached to glycerol through an ester bond.

eukarya includes all the eukaryotic cells, that is, the cells contain a nucleus and other membrane-bound cell organelles.

they can be autotrophic as well as heterotrophic, unicellular as well as multicellular

they include kingdoms like protista, plantae, animalia, fungi et cetera.

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explanation:

i think the answer is a.keratin is the pigment responsible for skin color.