New measurements taken from sleeping people explain,at least in part,why dreams tend

to have such bizarre but vivid storylines.The findings deal a blow to the Freudian interpretation of dreams but leave open the possibility that some useful personal meaning can be extracted from them.The main purpose of dreams,however,the authors of the new study believe,is to test whether the brain has had enough sleep and,if so,to wake it up.The new results show that in sleep,the frontal lobes of the brain are shut down.In the absence of activity in these lobes,which integrate other information and make sense of the outside world,the sleeping brain's images are driven by its emotional centers.The content of these dreams may be vivid and gripping but lacks coherence.The new results are consistent with the theory that memories are consolidated during sleep.From the pattern of activity that was recorded,"it seems that memories already in the system are being read out and filed in terms of their emotional salience,with is an extremely interesting idea,"said Dr.J.Allan Hobson of Harvard Medical School.The new measurements were made by applying the technique known as PET scanning to sleeping subjects.The biologists focused on the two forms of sleep,known as slow-wave sleep and REM sleep.REM sleep,so named because of the rapid eyeball movements that occur then,takes palce about four times during the night and is the phase from which the most vivid dreams are recalled.

问题：Accoding to this study,the purpose of the dreams is to ()

A、test if the brain has had enough sleep

B、show the dreams bizarre but vivid storylines

C、prove the correctness of the Freudian interpretation of dreams

D、extract some useful personal meanings from the dreams