A new study says one part of the human brain may become smaller as the result of a condition known as jet lag. Jet lag results from flying long distances in an airplane. Jet lag interferes with a person's normal times for sleeping and waking. People with jet lag may feel extremely tired for several days. They also may have problems thinking clearly and remembering.
Kwangwook Cho is a researcher at the University of Bristol in Britain. He reported the findings of his jet lag study in the publication Nature Neuroscience.
The study involved twenty young women who worked for international airlines. The women had served passengers on airplanes for five years. These flight attendants flew across many countries and at least seven time zones. In the study, the flight attendants had different amounts of time to recover from jet lag. Half the women spent five days or fewer in their home areas between long flights. The other half spent more than fourteen days in their home areas.
Mister Cho took some fluid from the women's mouths to measure levels of a hormone that increases during stress. He tested them to see if they could remember where black spots appeared on a computer screen. And he took pictures of their brains using magnetic resonance imaging. This is a way to measure the size of the brain's temporal lobes.
It was found that the women who had less time between flights had smaller right temporal lobes. This area of the brain deals with recognizing and remembering what is seen. The same group performed worse and had slower reaction times on the visual memory test. And their saliva samples showed higher levels of stress hormones.
Mister Cho says he believes the brain needs at least ten days to recover after a long trip. He says airline workers told him their ability to remember got worse after working on planes for about four years. Other studies have shown that increased feelings of stress can cause a loss of cells in the part of the brain that controls memory.
Scientists say more tests are needed to study the effects of jet lag on the brain. They want to find out if too much jet lag could permanently affect memory.
According to the text, jet lag _____.

A．can cause difficulties in speaking

B．can make people feel tired for a few weeks

C．is the illness only found in people who work on the airplanes

D．can be caused by flying over several time zones in an airplane

It is inferred that more tests need to be done because _____.

A．the conclusion was questioned by many scientists

B．scientists fear that his research is not done properly

C．every scientific conclusion needs the support from many tests

D．the woman who were studied in the research were not healthy

What is the subject discussed in the test?

A．The cause of jet lag.

B．A story of a group of flight attendance.

C．A research about the effects of jet lag on the brain.

D．The importance of having enough rest after long flights.