A. In recent years usage of fossil-fuel to produce electricity, especially coal, has significantly decreased.
here, we are assimilating coal as a sub-dimension of electricity, that is wrong
B. In recent years fossil-fuel usage, especially coal, to produce electricity has significantly decreased.
here, we are assimilating usage to be coal, which is incorrect, Wrong answer
C. For producing electricity, usage of fossil-fuel, especially of coal, in recent years have significantly decreased.
normally it should be that "usage" of coal, Wrong answer choice
D. To produce electricity, fossil-fuel usage, especially that of coal, has significantly decreased in recent years.
this is the correct answer, the conveyed meaning is respected and the two things compared are logical and parallel
E. Usage of fossil fuel, especially of coal, to produce electricity has significantly decreased in recent years.
to produce electricity should be followed by a coma, Wrong asnwer