A．How to safeguard the computer network.
B．How to steal top secret files from a military base.
C．How to make modern devices broadcast invisible, inaudible signals.
D．How to use an FM radio to detect the invisible, inaudible signals.

A．Because it costs $ 77 billion to develop further.
B．Because it even puts data in offline devices in danger.
C．Because it aims at nuclear facilities and military bases.
D．Because it is revealed to reporters and the public.

A．By getting all the devices off the Internet.
B．By stopping using all the advanced laser printers.
C．By installing high-tech anti-hacking softwares.
D．By using an AM radio to detect the signals.