Match the following:

Group 1	Group 2
P. Hall petch relation	1. Bulk diffusion between grain boundaries
Q. Orowan mechanism	2. Fracture of brittle materials
R. Nabarro-Herring creep	3. Grain boundary strengthening
S. Griffith criterion	4. Dispersion strengthening

A. P-1, Q-2, R-3, S-4

B. P-2, Q-3, R-4, S-1

C. P-4, Q-1, R-2, S-3

D. P-3, Q-4, R-1, S-2

Answer: Option D