如图所示的伏安法测电阻电路中，电压表的内阻为4kΩ，读数为4V；电流表的内阻为10Ω，读数为5mA．待测电阻R的真实值等于（   ）

Decision-making under Stress

    A new review based on a research shows that acute stress affects the way the brain considers the advantages and disadvantages, causing it to focus on pleasure and ignore the possible negative (负面的) consequences of a decision.

     The research suggests that stress may change the way people make choices in predictable ways.

    “Stress affects how people learn,” says Professor Mara Mather. “People learn better about positive than negative outcomes under stress.”

    For example, two recent studies looked at how people learned to connect images(影像) with either rewards or punishments. In one experiment, some of the participants were first stressed by having to give a speech and do difficult math problems in front of an audience; in the other, some were stressed by having to keep their hands in ice water. In both cases, the stressed participants remembered the rewarded material more accurately and the punished material less accurately than those who hadn't gone through the stress.

    This phenomenon is likely not surprising to anyone who has tried to resist eating cookies or smoking a cigarette while under stress –at those moments, only the pleasure associated with such activities comes to mind. But the findings further suggest that stress may bring about a double effect. Not only are rewarding experiences remembered better, but negative consequences are also easily recalled.

    The research also found that stress appears to affect decision-making differently in men and women. While both men and women tend to focus on rewards and less on consequences under stress, their responses to risk turn out to be different.

    Men who had been stressed by the cold-water task tended to take more risks in the experiment while women responded in the opposite way. In stressful situations in which risk-taking can pay off big, men may tend to do better, when caution weighs more, however, women will win.

    This tendency to slow down and become more cautious when decisions are risky might also help explain why women are less likely to become addicted than men: they may more often avoid making the risky choices that eventually harden into addiction.

    Jia Meng used to keep a diary in Chinese. But one year ago, the 14-year-old girl from Heilongjiang Province began to write her diary in English, because Jia found her mother was reading her diary secretly. She changed the language because her mother can't read English. “It's like killing two birds with one stone.” said Jia, “My private things become safe and my English improves a lot.”

    Jia's mother is not the only mom who reads her child's diary. Recently, Renmin University of China had a survey among over 23,000 parents. The results show that 40% of parents read their children's sectects. That's why many teenagers try to find ways to protect their privacy(隐私).

    Wu Lei, 15, of Shanxi, keeps a diary, too. But he doesn't write it on paper. He writes online which he thinks is perfectly safe because his parents know nothing about the Internet.

    Lu Huan, 13, of Guangdong, said her parents always secretly listened to the talk between her friends and her on the telephone in their room. To solve this problem, Lu asked her parents to buy her a mobile phone.

    “Parents want to know what is going on in their children's lives,” said Shao Xiazhen, a teenage expert in Beijing. “But sometimes they go about it the wrong way.” Shao suggested to teenagers that instead of hiding their secrets, talking to parents should be a better solution. “If your parents know that you are safe, they'll let you keep your secrets.”

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