A、Most of them work only at room temperature. B、Most of them work only at freezing temperature. C、Most of them work only at extr

(5) Scientists may have just given hydrogen a squeeze strong enough to turn it into a metal. The important point here is that they "may" have. In fact, some critics strongly dispute the new claim.
    (6) Under extremely high pressures hydrogen may become reflective. Researchers at Harvard University in Cambridge, Mass, have just claimed to have seen it. That reflectivity is a key trait of metals. Their feat required compressing hydrogen to 4.9 million times atmospheric pressure.
    If correct, this crushing work would end a decades-long search for a material that could have unusual properties, such as superconductivity—the ability to conduct electricity without resistance.
    (7) Most superconductors work only at extremely cold temperatures. But some scientists have calculated that metallic hydrogen might prove a relatively high-temperature superconductor. It might have this trait even at room temperature—higher than any other known superconductor. If so, the new discovery would raise hopes that superconducting metallic hydrogen could be used in power lines. That could make transmission of electricity vastly more efficient.
Questions 5 to 7 are based on the news report you have just heard.
5. What is this news report mainly about?
6. How can we make hydrogen become reflective according to the news report?
7. What do we learn about superconductors?