What does "X" represent in the following symbol? 
X
Definitions:
Thrombin
An enzyme in blood plasma that causes the clotting of blood by converting fibrinogen to fibrin.
Phagocytotic Cells
Cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells.
Monocytes
A form of leukocyte crucial to the immune system, as it evolves into macrophages and dendritic cells.
Neutrophils
A type of white blood cell that helps the body fight infections by engulfing and destroying bacteria and fungi.
Q15: an atom that has lost an electron
Q23: Which consumer segment is most likely to
Q25: French- and English-speaking Canadians agree about most
Q42: Culture,a concept crucial to the understanding of
Q58: What is the chemical symbol for chlorine?<br>A)
Q76: Katrina really likes a new line of
Q108: List the age cohorts discussed in the
Q110: Nathalie has very long hair,and brushes it
Q111: In which orbital below would an electron
Q116: Calculate the frequency of the light emitted