Jonas is a veteran of the war in iraq. he suffers from posttraumatic stress disorder (ptsd). now, back home in a quiet california neighborhood, he jumps when he hears a firecracker or a car backfire. in the terminology of classical conditioning, these sounds are best thought of as stimuli.

Conditioned stimuli.

Explanation:

Conditioned stimulus may also defined as a type of the neutral stimulus. In classical conditioning the conditioned stimulus combines with strong stimulus and generates a strong response.

Jonas suffers from post traumatic stress disorder and was the veteran of the war in Iraq. He jumps whenever he hears the car backfire. Here, the sounds acts as the conditioned stimuli because it is a neutral stimulus and does not generates the strong response.  

Thus, the answer is conditioned stimuli.