Answer:
C). Thunder; lightning.
Step-by-step explanation:
Conditioned stimulus is described as the outcome of a learned behavior that primarily functions to trigger the specific conditioned response while the unconditioned stimulus is characterized as the naturally occurring stimulus that evokes a response automatically without any prior learning.
In the given example, the 'thunder' would be the unconditioned stimulus as it evokes a natural and unconditioned response from Samantha i.e. 'her jumping' while the 'lightning' exemplifies the 'conditioned stimulus' as it evokes a learned response which she has learnt from her previous experience and displayed even before hearing the thunder actually. It implies that her latter behavior was a learned response. Thus, option C is the correct answer.