Final answer:
The correct option is A. The word that describes both 'caused by heat' as an adjective and 'a rising current of warm air' as a noun is 'thermal'. It is related to concepts like thermal energy, convection, and thermal pollution.
Step-by-step explanation:
The word that can be used as an adjective to mean 'caused by heat' and as a noun to symbolize 'a rising current of warm air used by hang gliders' is thermal. This term is directly associated with thermal energy, which refers to the energy possessed by an object due to the movement of its particles and can cause various phenomena such as warm air rising. Convection is a process that perfectly illustrates the principle of thermal movement, where heat is transferred through fluids (gases and liquids).
This principle is evident in natural occurrences like thunderstorms, or in man-made devices like hot air balloons. Hot air being less dense rises, and this is the principle that hang gliders use to stay aloft. Both thermal pollution and thermal energy are related to the adjective/noun in question. As an environmental concern, thermal pollution occurs when heated substances, usually water, are released into natural bodies, affecting their temperature.