2. case study __________

A、the permanence of beauty

B、the permanence of love

C、the permanence of art

D、the permanence of urn

If a super-flu strikes, face masks may not protect you. Whether widespread use of masks will help, or harm, during the next worldwide flu outbreak is a question that researchers are studying furiously. No results have come from their mask research yet. However, the government says people should consider wearing them in certain situations anyway, just in case.

But it's a question the public keeps asking while the government are making preparations for the next flu pandemic. So the Centers for Disease Control and Prevention (CDC) came up with preliminary guidelines. "We don't want people wearing them everywhere, " said the CDC. "The overall recommendation really is to avoid exposure. "

When that's not possible, the guidelines say to consider wearing a simple surgical mask if you are in one of the three following situations. First, you're healthy and can't avoid going to a crowded place. Second, you're sick and think you may have close contract with the healthy, such as a family member checking on you. Third, you live with someone who's sick and thus might be in the early stages of infection, but still need to go out.

Influenza (流行性感冒) pandemics (全国流行的) can strike (打击) when the easy-to-mutate flu virus shifts to a strain that people never have experience D. Scientists cannot predict when the next pandemic will arrive, although concern is rising that the Asian bird flu might trigger one if it starts spreading easily from person to person.

During the flu pandemic, you should protect yourself. Avoid crowds, and avoid close contract with the sick unless you must care for someone. Why can't mask added to this self-protection list？ Because they help trap virus-laden droplets flying through the air with a cough or sneeze (打喷嚏). Simple surgical masks only filter the larger droplets (小滴). Besides, the CDC is afraid？ masks may create a false sense of security. Perhaps someone who should have stayed home would don an ill-fitting (不合的) mask and hop on the subway instead.

Nor does flu only spread through the air. Say someone covers a sneeze with his or her hand, then touches a doorknob or subway pole. If you touch that spot next and then put germy hands on your nose or mouth, you've been exposed. It's harder to rub your nose while wearing a mask and so your face may get pretty sweaty under masks. You reach under to wipe that sweat, and may transfer germs caught on the outside of the mask straight to the nose. These are the problems face masks may create for their users.

Whether people should or should not use face masks still remains a question. The general public has to wait patiently for the results of the mask research scientists are still doing.

A. Reasons for Excluding Masks from the Self-protection List

B. Effort to Stop Flu Spreading

C. When to Use Face Masks

D. Guidelines on Mask Use

E. Warnings from the CDC

F. Danger of Infection through Germy Hands and Masks

Paragraph 2 ______

A、Sensitivity, specificity and positive likelihood ratio

B、Correlation coefficient, correct index and likelihood ratio

C、Correlation coefficient, coefficient of variation and Kappa value

D、Predicted value, Youden index and coincidence rate