单项选择题
Behavioral psychologists apprehend that conditioned fear responses to atone previously paired with a shock diminish, if the tone is repeatedly presented without the shock, a process known as extinction. Since Parlor it has been hypothesized that this extinction does not erase conditioning, but forms a new memory. Research has now demonstrated that destruction of the infralimbic cortice blocks recall of fear extinction, indicating that it might store long-term extinction memory. Infralimbic neurons recorded during fear conditioning and extinction fire to the tone only when rats are recalling extinction on the following day, and rats indicating the least fear responses also demonstrate the greatest increase in infralimbic tone responses. Conditioned tones paired with brief electrical stimulation of infralimbic cortex elicit low fear responses in rats that have not undergone extinction. Thus, stimulation resembling extinction-induced infralimbic tone responses is able to simulate extinction memory.
According to the passage, behavioral psychologists studying the extinction process have discerned which of the following（） A．The exact length of time required for a fear response to become extinct in a human subject
B．The effect of tone conditioning in comparison with other forms of stimuli
C．The possible effects of surgical operations on the infralimbic cortice
D．The potential of tone conditioning in treating undesirable fear responses
E．The limits of Pavlov’s contribution to modern behavioral psychology