Do you have trouble getting started in the morning? Do you have problems learning early in the day? If you do, you are not alone, ___ They learn better at night than they do in the morning.
To investigate when cockroaches(蟑螂) learn best, researchers at Vanderbill University tested the insects for which odor(peppermint 薄荷 or vanilla 香草) they preferred. Most cockroaches preferred the smell of vanilla to that of peppermint at all times. __ Therefore, the scientists trained the cockroaches to prefer the peppermint smell by rewarding the insects with a taste of sugar water when they approached a peppermint smell. ___
When the cockroaches were trained at night, they remembered the new associations(peppermint＝sugar water; vanilla＝salt water) for up to 48 hours. However, if the cockroaches were trained in the morning, they quickly forgot which smell went with which water. ___
So, cockroaches learn better at night than they do in the morning. __ Because of this, it is likely that information they gather at night will be more useful to them. These experiments provide some clues about the interactions between body rhythms, learning and memory.

A．When these insects moved toward a vanilla smell, on the other hand, they were punished with a taste of salt.

B．This result thus shows that the time when they were trained decided the effect of their learning.

C．They are often more active and tend to search for food during the night.

D．They were also found to like sugar water, but not salt water.

E．Cockroaches have the same problem!
F．But they prefer warm conditions found within buildings.
G．Pest species adapt easily to their environment.