The most appropriate answer would be A. Serves as an identifier or marker to help cells recognize & distinguish themselves from one another.
The given molecule would belong to special class of proteins called as cell surface marker proteins or antigens. These are special proteins expressed on the membrane of the cell and serve as identifiers or markers of specific cell types.
These markers along with surface receptors help in cell-to-cell interaction and thus help the biological systems to work in coordinated fashion.
In addition, they help the immune system to distinguish between self and non-self or foreign cells. Immune system cells such as memory T and B cells, cytokines etc recognize specific cell surface proteins or antigens present on bacteria or other invading microorganism.
<span>"It is likely you are suffering from airborne allergies that are unfamiliar to your body. I recommend that you see your acupuncturist and seek help for these symptoms since you prefer to not to take medication".</span>
