Answer:
a. unconditioned stimulus
Explanation:
Unconditioned stimulus: In psychology, the term "unconditioned stimulus" is described as one of the parts in the classical conditioning theory and is also denoted as UCS or US. It is defined as one of the stimuli that tend to trigger a particular response unreservedly what so ever is being presented without being trained in past and hence triggers the unconditioned response or UCR or UR.
In the question above, the given statement signifies the "unconditioned stimulus".
<span>The best rule to follow in applying operant conditioning to your own life is to is a form of associative learning in which behaviors are triggered by associations with events in the environment. In classical conditioning it is learning in which an organism comes to ASSOCIATE one stimulus with another.</span>