A vapour absorption system does the same overall job as a normal vapour compression fridge, moving heat from a cold space to a warm one, but it uses a heat driven absorber-generator pair instead of an electrically driven compressor. This needs two fluids that mix well with each other: one that boils off at low temperature in the evaporator to produce the cooling effect (the refrigerant), and a second fluid that soaks up the refrigerant vapour in the absorber and carries it round to the generator where heat drives it back out again (the absorbent). The two common industrial pairs are ammonia with water, and water with lithium bromide. In the first pair, ammonia is the one that evaporates and produces cooling, so ammonia is the refrigerant and water is the absorbent. In the second pair, water itself is the one evaporating, so there water is the refrigerant and lithium bromide is the absorbent, the opposite roles from option (B), which is why that option is wrong even though the two chemicals are correct. Matching refrigerant then absorbent in that exact order gives ammonia and water, option (D).