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A
All hazmat can be loaded together in any combination
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B
Some hazardous materials cannot be transported together because they could react dangerously — for example, flammables cannot be loaded with oxidizers, and poisons cannot be loaded with foodstuffs
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C
Compatibility only applies to explosives
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D
Compatibility means the cargo fits in the trailer space
Why this is the answer
HAZMAT COMPATIBILITY rules (the 'Segregation and Separation Table' in 49 CFR) prevent dangerous reactions between different hazardous materials that might come into contact in the event of a leak, spill, or vehicle accident. WHY INCOMPATIBLE MATERIALS ARE DANGEROUS TOGETHER: Some combinations cause fires, explosions, toxic gas releases, or violent chemical reactions when mixed. SPECIFIC PROHIBITED COMBINATIONS: FLAMMABLES and OXIDIZERS (Class 5.1/5.2): Oxidizers accelerate burning and can cause spontaneous ignition of flammables — these must be kept separate; POISONS (Class 6.1) and FOODSTUFFS: Poison materials cannot be transported with food, feed, or other edibles — contamination risk; RADIOACTIVE materials have specific segregation requirements from certain other cargo; ORGANIC PEROXIDES and certain reactive materials; EXPLOSIVES have extensive segregation requirements from almost all other hazmat classes. THE CHART: 49 CFR Part 177.848 contains the segregation table — 'X' means forbidden in the same vehicle; 'O' means forbidden in the same vehicle unless separated by specific distances or barriers; blank means no segregation required. PRACTICAL CHECK: Before loading a mixed hazmat shipment, the driver and carrier must verify compatibility. The shipper's paperwork should indicate segregation requirements. RESPONSIBILITY: The shipper classifies and provides compatibility information; the carrier and driver must not load incompatible materials and must verify before accepting a load.
Source: FMCSA CDL Manual, Chapter 9, Hazardous Materials, Compatibility and Segregation