How can the overall order of a reaction be determined?

Question

A. Add the exponents in an equilibrium constant expression.
B. Add the coefficients in the balanced equation.
C. Count the number of different reactants.
D. Examine experimental data for the reaction over time.

Answer 1

http://www.chemguide.co.uk/physical/basicrates/orders.html

Answer 2

I believe that the answer is D