If f(x)= 2x² +4, which of the following will calculate the derivative of f(x)?

a. ([2(x+△x)² +4] - (2x² +4))/ △x
b. lim △x->0 ((2x² +4 +△x) - (2x² +4))/ △x
c. lim △x->0 ([2(x+△x)² +4] - (2x² +4))/ △x
d. ((2x² +4 +△x) - (2x² +4))/△x