Tech giants Apple and Google are teaming up to create a system that would let smartphone users know when they've come into contact with someone who has COVID-19.
The technology would rely on the Bluetooth signals that smartphones can both send out and receive.If a person tests positive for COVID-19，they could inform public health authorities through an app.Those public health apps would then warn anyone whose smartphones had come near the infected person's phone within 14 days.
The technology could be used on both Google Android phones and Apple iPhones.The companies insist that they will preserve smartphone users' privacy.Smartphone users must choose to use it independently.The software will not collect data on users' physical locations or their personally identifiable information.People who test positive would remain anonymous（匿名的），both to the people who came in contact with them and to Apple and Google.
The American Civil Liberties Union（ACLU） has warned that using cellphone data to address the pandemic（流行病） may carry risks of "invasions of privacy,abuse of information,and stigmatization（污名化）".
An adviser from ACLU，Jennifer Granick said that the joint Apple and Google project "appears to mitigate the worst privacy and concentration risks,but there is still room for improvement." She added that contact tracking apps should be "voluntary and used only for public health purposes and only for the period of this pandemic."
Google and Apple say their technology will be used only by public health authorities to track the spread of COVID-19.
A team at MIT also has been working on a contact-tracking system that similarly uses Bluetooth signals to identify when people have come near each other.
Apple and Google are carrying out their contact-tracking technology in two steps.In mid-May,they will release（发布）software that will let public health authorities build apps that exchange information via Bluetooth.In the coming months,they will update their operating systems so phones can share information without having to install an app.



What can we learn from the text？ ______

A. The system knows when a person has COVID-19.
B. The technology can be used in any type of phone.
C. The companies promise to ensure the users' privacy.
D. Using smartphone data will definitely bring risks to users.

What does the underlined word "mitigate" in Paragraph 5 refer to？ ______

A. Solve.
B. Reduce.
C. Increase.
D. Take.

Which word best describes the author's attitude to contact tracking app？ ______

A. Doubtful.
B. Unconcerned
C. Caring.
D. Objective.

What's the author's purpose of writing this text？ ______

A. To inform the readers of a new technology.
B. To recommend the readers to use a new app.
C. To warn the users of the risks of the software.
D. To praise Tech giants for their contribution.