The correct answer is C) Cargo temperature may be taken by portable thermometers. This is correct because the cargo temperature needs to be monitored to ensure the molten sulfur is maintained at the proper temperature for safe handling and transfer. Portable thermometers provide a simple way to measure the cargo temperature directly, rather than relying on pressure or other indirect methods. The other answer choices are incorrect: A) The pressure in the heating coils must be greater than the cargo pressure to prevent leakage. B) Two portable toxic vapor detectors are not required for a sulfur cargo. D) The ventilation system must maintain H2S vapor concentration below explosive levels, not at 1.85% or more.