A、To test the drug on many more people with heart attacks. B、To test those who suffer from heart attacks. C、To test the doctors

An important new study reports that doctors now have a new drug called TPA for heart attacks. It may be better than any other heart drug.
    Many doctors have been using a drug called Streptokinase, which sometimes causes problems for patients. It can even cause bleeding in the brain. Streptokinase can save about 1/3 of the people with heart attacks. But TPA will save about 2/3. This means many people. About 1.5 million Americans have heart attacks every year.
    One reason TPA can help more people is because of time. This new drug is easier and faster to use. It will give doctors more time in hospitals. Then they can study the problem well. People with heart problems can also keep some TPA at home. When a heart attack starts, they can take some TPA right away. Then they will have time to get to the hospital. This is important because about 860,000 people in the United States die before they get to the hospital.
    There is another reason why TPA is good news for people with heart attacks. According to the study, it is much safer. It does not cause other problems like Streptokinase. TPA works only on the heart. It does not have an effect on the blood or cause bleeding.
    Doctors plan to do more studies about TPA. They need to test this new drug on many more people with heart attacks. But in a few years, many doctors and hospitals will probably start using this exciting new drug.
21. What problem can Streptokinase cause?
22. According to the talk, how many Americans have heart attacks every year?
23. Which is NOT mentioned as an advantage of TPA?
24. Which of the following is true?
25. Why need doctors plan to do more studies about TPA?