A.
The United States refers to a COMPARTMENT to be a space of an aircraft that is formed by walls or bulkheads with a solid flooring and ceiling.

A normal wide-bodied aircraft will have two COMPARTMENTS in the lower Dec , i.e., the FWD COMPARTMENT and the AFT COMPARTMENT. IATA in its Airport Handling Manual defines the same space as a HOLD, and a COMPARTMENT is an area within the HOLD.

Therefore, according to IATA definition, a wide-bodied aircraft will normally have 2 HOLDs in the lower Dec , the FWD HOLD and AFT HOLD. Within the FWD HOLD, there are two COMPARTMENTS, FWD 1 and FWD 2 COMPARTMENTS. In the AFT HOLD, there are 3 compartments, AFT 3, AFT 4 and BULK COMPARTMENTS. Take caution as the US DOT definition is not the same as IATA.