lymphocytes are specialized T cell ,B cell, and natural killer cell .
these cells are distinguished from other lymphocytes by a protein on their surface known as the B cell receptor .these protein is specialized to recognize and attach to specific antigens.
Answer:
An index fossil is a fossil used to determine the age of the sediments in which it is found. When quickly approximating the age of new finds, an archaeologist looks at the rocks in which it is buried, as those sediments would have been on the surface at the time of the death of the pre-historic creature.
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A group of tissue that work together is a organ
