All organisms descended from a common ancestor
The biological basis for assigning all human beings into a singe species is that there so many, even tons of living organisms living on earth. These organisms differ in their external and internal organs and so to differentiate them from them, they are being classified into kingdoms then classes then phylums then family.
If blood typing is not available in an emergency situation, O-Negative blood is universally accepted by all blood types because it is absent of any antibodies. Therefore, if O-Neg blood is on hand in emergency situations, it can be given to anyone.
The correct answer is natural selection. C is the answer!
Bacteria has a stronger resistance that usually produces even more resistant bacteria, and the cycle just repeats itself, making more and more resistant bacteria. This process is called Natural Selection.
Hope that helped!
-Chris
