API RP 571 notes that for detecting existing cracks or flaws that may lead to brittle fracture, especially those that initiate at welds or surface stress points:
"Wet fluorescent magnetic-particle inspection is highly effective for detecting surface-breaking flaws in ferromagnetic materials that are susceptible to brittle fracture."
"It is sensitive to tight cracks and surface discontinuities that may serve as initiation sites for brittle fracture." (Reference: API RP 571, Section 4.2.1.2 - Brittle Fracture) Therefore, option A is correct as it is the most effective NDE technique for detecting early signs of brittle cracking.