题目内容：

    Printed circuit boards are vital components of modern electronics. However, once they have served their purpose, they are often burned or buried in landfills, polluting the air, soil and water. Most concerning are the flame retardants （阻燃剂）added to printed circuit boards to keep them from catching fire. Now, researchers reporting in ACS Sustainable Chemistry & Engineering have developed a ball-milling method to break down these potentially harmful compounds enabling safer disposal （处理）.

Composed of 30% metallic and 70% nonmetallic particles, printed circuit boards support and connect all of the electrical components of a device. Metallic components can be recovered from circuit boards easily using traditional methods leaving behind nonmetallic particles including those flame retardants and other additives. Scientists have found that compounds in those flame retardants can do harm to people's health, especially to those women who are pregnant. Therefore researchers have been wanting to develop a new method to remove the flame retardants from waste printed circuit boards so that they wouldn't do harm to people and the environment.

The researchers broke down printed circuit boards and removed the metallic components. Then，they put the nonmetallic particles into a ball mill — a rotating （旋转的）machine that uses hard stone balls to make materials into very small pieces. They also added iron powder, which prior studies had shown was helpful for removing chemicals from organic compounds. After ball-milling, the harmful chemicals on the surface of the particles had decreased by 50%・ The researchers determined that during the ball-milling process, iron transferred electrons to flame retardant compounds causing the internal structure to stretch and break.

The authors acknowledge funding from the 111 Project, the Natural Science Foundation of Guangdong Province, China and the Pearl River Star of Science and Technology.

1.People are concerned most about the flame retardants because

A.they are harmful and hard to remove B.they keep circuit boards from catching fire

C.they make up the largest part in electronics D.they are mixed up with other components

2.What is the function of the printed circuit board?

A.Making electronics small and light. B.Preventing electronics catching fire.

C.Connecting all electrical components, D.Allowing easy disposal after being used,

3.What does the author mainly intend to tell us in paragraph 3?

A.How to operate the ball milk B.The ball-milling process and its result.

C.The high efficiency of the new method. D.Why iron powder is added to the process.

4.What can we infer from the last paragraph?

A.The authors are short of money.

B.Over 100 projects support the authors,

C.The researchers will make much money.

D.The ball-milling method is promising.