Boiling water is a physical change. This is because the water that is being changed into a gas, and can be changed back. Bohr proposed a theory that helped make the blueprint for the atomic model. Gold is a soft but heavy metal, and reflects light with a green/blue hue. Gold is a shiny yellow to canary yellow in colour, and is often confused with pyrite, or 'fool's gold'. The particles in a solid vibrate in place, and are very close together. When one atom of carbon and two of oxygen meet, the make a bond that in turn creates CO2 or carbon dioxide. I hope I helped. :)
A sounds correct
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<span>Cytotoxic t-cell subpopulations are specialized to combat intracellular pathogens, whereas helper t-cell subpopulations are specialized to combat extracellular pathogens.
</span>Cytotoxic t-cell are CD8+ cells. Cytotoxic t-cell uses granzymes to <span>kill </span><span>intracellular bacteria, that lives in the cytosol such as viruses. They identify the pathogen forgein peptids that are bounded to MHC-I on the cell surface.
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cd4+ T helper (Th) cells include Th1, Th2, and Th17 cells. They contribute to aliergic reactions and fighting extracellular parasites.
