Viruses is the answer to this
A hypersensitive reaction to a specific antigen in the environment is a(n) _ALLERGY_.
Might be gene regulation, the process of turning genes on and off in normal development
<span>One that is made of nitrogen and hydrogen is definitely inorganic. Inorganic has these molecules in them.</span>
Doctors inject medicines in veins because veins are more accessible and donot have high pressure due to which there is no risk of blood backing up with into the infused fluid.
However there are some cases when medicine is injected in artery but a lot of precautions needs to be taken while doing so.