Find the derivative f'(x) of the function f(x) = 2x^3 - x^2 - x + 2 using the definition of a derivative. Choose the correct option.
Option A: f'(x) = 6x^2 - 2x - 1
Option B: f'(x) = 6x^2 - 2x + 1
Option C: f'(x) = 6x^2 + 2x - 1
Option D: f'(x) = 6x^2 + 2x + 1