A、200. B、300. C、400. D、Millions of. B从录音中可知The researchers tested blood from about 300 people，因此B为正确答案。

Cancer is a leading cause of death around the world.
   When it comes to cancer, the sooner you know you have it, the better your chances of surviving. A new blood test could change the way doctors and researchers find cancer in patients. Researchers say the test could provide clues to the early forms of the disease. Scientists at the University of Swansea in Wales came up with the idea.
   Gareth Jenkins is a professor at the university. He says he and his team did not look for cancer. They instead looked for a by-product of cancer. They looked for, what Jenkins calls, the collateral damage of cancer — the damage left by the disease. In this case, the by-product was mutated red blood cells.
   The researchers used normal laboratory equipment to perform the test. This equipment looks for changes in the structure of millions of red blood cells. Those mutated cells lack a surface protein that healthy cells normally have.
   The researchers tested blood from about 300 people, all of whom have cancer of the esophagus. Patients with esophageal cancer have high levels of mutated red blood cells. Jenkins says that at this point he is not sure if other cancers would produce similar results.
   The hope is that the new test and other non-invasive methods could one day become part of commonly used medical methods. He says that using a battery, or series, of tests will be the best way to find out if a person has cancer.
   These new technologies could save millions of lives.
Questions 21 -25 are based on the passage you have just heard.
21. What does the passage mainly talk about?
22. Who is Gareth Jenkins?
23. What does the new test do?
24. What’s the difference between the damaged red blood cells and the normal ones?
25. How many patients did the new research test?