Answer :
C) Atom
Actual answer should be element but depends on the way you interpret the question and the options given to answer it
Explanation :
Atom is the most basic unit of any substance and is what molecules are made of.
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There are many factors which contributes as to how a machine will be processing the input energy and convert it to output energy. Even with identical mechanism, these factors will have major effect on the output. Some factors are deflection, friction and wear. Some system maybe exposed to poor lubrication than the other which'll produce more friction and wear thus lower mechanical advantage.