from 2014 to 2015, Rao designed a new testing system that resulted in her being named America's Top Young Scientist for 2017.

　　Rao had been following the water problem for about two years. She was amazed by the number of people affected by lead pollution in water and wanted to do something to change this. Gitanjali spent months trying to convince local high schools and colleges to give her lab time to continue her experiment. At home, Gitanjali worked on her project in the "science room" she asked her parents to create for her. Rao has created a device that uses three parts: a cartridge, a Bluetooth reader and an app. To put it simply, the cartridge contains carbon nanotubes（纳米管） that react to lead. This reaction is then registered by the Bluetooth reader, which sends a signal to a mobile app that can tell you immediately if your water is safe to drink.

　　Rao appropriately named the device Tethys after the Greek goddess of fresh water, and is hoping to make a little improvement to get the device on the market. While we may not be aware of any lead pollution present in our aging pipelines, lead poisoning can cause delays in physical and mental development. With Rao believing that the "purpose of science is to make a difference", her incredible invention could make a difference to millions of people in the United States.

24. What do we know about Rao's device?

　　A. It's cheap and quick. B. It's cheap and inaccurate.

　　C. It's expensive and reliable. D. It's portable and time-consuming.

25. What made Rao have the idea of designing the device?

　　A. Her parents' suggestions. B. The name of the Greek goddess.

　　C. Her interest in settling real problems. D. The water pollution litigation in Flint.

26. What do the carbon nanotubes function as?

　　A. Sending immediate signals. B. Recording the reaction results.

　　C. Detecting the presence of lead. D. Showing the water quality results.

27. What does the author think of Rao's invention?

A. It will lead Rao to make a fortune.