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.  

The correct answer to this open question is the following.

Although there are no options attached, we can say the following.

Two or more freely interacting individuals who share norms, share goals and have a common identity form a group.

That is why people gather together in groups. Because they have similarities and common values. They enjoy to stay together, talk, exchange ideas and support each other. If this group goes one step beyond, we would have been talking about a formal group that was formed to do a specific task productively. Commonly, these groups are part of organizations and are directed by someone who is the leader.