Jonas is a veteran of the war in iraq. he suffers from posttraumatic stress disorder (ptsd). at present, he is back home in a quiet california neighborhood, and jumps when he hears a firecracker or a car backfire. in the terminology of classical conditioning, these sounds are most likely to be referred to as stimuli.

conditioned  

Explanation:

Conditioned stimuli: In the classical conditioning, give by Ivan Pavlov, the conditioned stimulus is a formerly neutral stimulus triggers a conditioned response after beseeming associated with the unconditioned stimulus.

According to the question, Jonas who has suffered from post-traumatic stress disorder got scared when he hears a firecracker or a car backfire because he might relate this with the previous incident.

The most accurate answer is External Stimuli

Explanation:

The external stimuli is directly related to the hypervigilance and reactivity symptoms. These symptoms are described when a person startles easily and, he usually feels stressed. In addition to this, this person may feel constantly nervous among present situations or stimuli: This can take place when the subject lives something that can bring memories of that traumatic experience.  

answer; i believe the correct answer is (crops);