Answer:
Tense and upset at flashing red lights
Explanation:
Conditioned stimulus: In psychology, the term "conditioned stimulus" is one of the different elements in the theory of "classical conditioning" which was proposed by Ivan Pavlov while experimenting with dogs.
The "conditioned stimulus" is described as a formerly neutral stimulus that tends to trigger or give rise to a "conditioned response" after becoming connected with the "unconditioned stimulus".
In the question above, the conditioned stimulus is "tense & upset at flashing of red lights".