In API RP 571, under the section Polythionic Acid Stress Corrosion Cracking, it is stated:
"Sensitization of austenitic stainless steels occurs when the material is exposed to temperatures in the range of
800°F to 1500°F (427°C to 816°C), which causes chromium carbide precipitation at grain boundaries, depleting the adjacent areas of chromium."
"Once sensitized, the steel becomes susceptible to attack in the presence of polythionic acids, particularly in environments containing sulfides and oxygen." (Reference: API RP 571, Section 4.2.2.5 - PTA SCC) This makes option B (750°F to 1500°F / 400°C to 815°C) the most accurate and standard-aligned answer.