For several years, scientists have been testing a substance called interferon(干扰素), a possible wonder drug that is proving to be effective in treating a variety of diseases, including virus infections, bacterial infections, and cancers. To date, the new drug has no side effect of great influence to discourage its use.  But in spite of its success, last year only one gram was produced in the entire world.
The reason for the shortage lies in the structure of interferon. A special protein, the interferon produced from one animal species cannot be used in treating another animal species. In other words, to treat human beings, only interferon produced by human beings may be used. The drug is produced by infecting white blood cells with a virus. Fortunately, it is so effective that the amount given to each patient each time is very small.
Unlike antibiotics (抗生素), interferon does not attack germs directly. Instead, it protects healthy cells from being infected, and prevents the reproduction of viruses within cells.
As you might conclude, one of the most special uses of interferon has been in the treatment of cancer. Dr. Hans Strander, a research physician at Sweden’s famous Karolinska Institute, has treated more than one hundred cancer patients with the new drug. Among a group of selected patients who had received operations for advanced cancer, half were given  traditional treatments and the other half were given interferon. Among those treated with interferon 70 percent of them remained alive over three years, as compared with only 10 to 30 percent among those who had received the traditional treatments.
In the United States, a large-scale project supported by the American Cancer Society is now under way. If the experiment were successful, interferon could become one of the greatest medical discoveries of our time.
What is the difference between antibiotics and interferon?

A．Interferon has serious side effects, while antibiotics do not.

B．Antibiotics kill germs by attacking them directly, while interferon does not.

C．Antibiotics are very effective, while the effect of interferon is limited.

D．They are different in structure, although they are both proteins.

According to the passage, if 170 cancer patients received interferon treatment, how many of them would remain alive over three years?

A．About 30.

B．About 50.

C．About 120.

D．About 70.

The passage tells us that ________.

A．it is difficult to produce interferon in large quantities because of its special structure.

B．interferon is produced widely in lots of countries.

C．few of the patients who had received traditional treatments remained alive.

D．most of the patients who received interferon also needed traditional treatments.