The correct answer is A) Cargo-hold moisture content is reduced by supplying relatively dry air from the outside and exhausting relatively humid air to the outside. This is the correct answer because dehumidification of cargo holds works by bringing in dry air from the outside and exhausting the more humid air from the cargo hold. The dry air helps absorb and remove excess moisture, thereby reducing the overall moisture content in the cargo hold. The other options are incorrect because they describe the opposite process, where the moisture content would either increase or not be reduced effectively.