Efficiency is
a.
the percentage of energy lost to the surroundings as heat.
b.
the percentage of energy that is actually used to perform work.
c.
the entire amount of energy.
d.
the time it takes for half of the energy to be used.

B: Efficiency is the percentage of energy that is actually used to perform work. 
 Efficiency is the (often measurable) ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without waste. In more mathematical or scientific terms, it is a measure of the extent to which input is well used for an intended task or function (output). Hope this helps! Please put Brainliest! 

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Full change in the electric plus system