How do perturbation methods estimate the change in k_eff due to small material property changes?

• A. Δk_eff ≈ ∑ (∂k_eff/∂p_i) Δp_i, computed with forward and adjoint fluxes
• B. Δk_eff = Δp_i
• C. Δk_eff is independent of properties
• D. Δk_eff uses only flux integrals

Answer: (A)