Answer:
Classical conditioning
Explanation:
Conditioning is the process of pairing two stimuli together such that if one stimulus can trigger a reaction, the other can do the same, too, simply by association.
Classical conditioning, which is also referred to as Pavlovian conditioning, is a learning process where neutral stimulus is associated with a biologically potent stimulus.
People have conditioned themselves through classical conditioning to always associate thunder with lightening.
Hence, once there is a lightening (neutral stimulus), there is the expectation of having thunder (biological potent stimulus)
