18. a dam generates electricity from water flowing downhill and is an example of how systems… a. violate the 2nd law of thermodynamics b. take advantage of energy flow from low to high c. violate the 3rd law of thermodynamics d. take advantage of energy flow from high to low

Hello!! 

When a dam generates electricity, it is doing so, ultimately from The second Law of Thermodynamics, taking advantage of energy flow from high to low.

So we can see the best choice here would be D. 
To take advantage of energy flow from high to low. 

Hope this helps! Any questions, please feel free to ask! Thank you kindly!

Dis the

stands for electromotive force and it is measured in volts. despite its name, it is not actually the force in the sense of being a "pushing" or "pulling" (not measured in newtons).an equation that relates emf,  ℰ,  to a battery's terminal voltage, v, current, i, and internal resistance, r, is    ℰ = v + irin this case, the emf can be interpreted as a voltage—a difference in electric potential.i would not say that it would be considered an energy. if emf can be defined as the energy/work per a unit charge from a battery or other electric source, then it is not strictly energy.