Since the Internet came into homes, the daily life has never been the same again. But the thing that worries most of us is that we can get viruses from the Internet. But can we catch viruses on our cell phones? A new study in the journal Science says yes, but the spread of such mobile software that can bring harm to our cell phones won't reach dangerous levels until more cell phones are on the same operating system. Computers are easily attacked by viruses because they share data, especially over the Internet. Of course, nowadays, more people are using their cell phones more and more frequently. They use them for emailing, text messaging and downloading troublesome ring tones, etc.,so it is obvious that cell phone viruses are a threat as well. Scientists used nameless call data from more than six million cell phone users to help model a possible outbreak. And they concluded that viruses that spread from phone to phone by Bluetooth are not much concerned, because users have to be in close physical relation for their phones to "see" one another. However, viruses that spread through multimedia messaging services can move much faster, because they can come in disguise , such as a cool tune sent by a friend. The good news is that to be effective, these viruses need their victims  to all use the same operating system, which not enough of us do. Because there is no Microsoft operating system for mobile phones, yet. Thank goodness. When   _  , cell phone viruses can be dangerous.
all the cell phones work on the same operating system Microsoft operating system for cell phones is created users can see each other on the phones Bluetooth is widely used
Question: Since the Internet came into homes, the daily life has never been the same again. But the thing that worries most of us is that we can get viruses from the Internet. But can we catch viruses on our cell phones? A new study in the journal Science says yes, but the spread of such mobile software that can bring harm to our cell phones won't reach dangerous levels until more cell phones are on the same operating system. Computers are easily attacked by viruses because they share data, especially over the Internet. Of course, nowadays, more people are using their cell phones more and more frequently. They use them for emailing, text messaging and downloading troublesome ring tones, etc.,so it is obvious that cell phone viruses are a threat as well. Scientists used nameless call data from more than six million cell phone users to help model a possible outbreak. And they concluded that viruses that spread from phone to phone by Bluetooth are not much concerned, because users have to be in close physical relation for their phones to "see" one another. However, viruses that spread through multimedia messaging services can move much faster, because they can come in disguise , such as a cool tune sent by a friend. The good news is that to be effective, these viruses need their victims  to all use the same operating system, which not enough of us do. Because there is no Microsoft operating system for mobile phones, yet. Thank goodness. When   _  , cell phone viruses can be dangerous.
A. all the cell phones work on the same operating system
B. Microsoft operating system for cell phones is created
C. users can see each other on the phones
D. Bluetooth is widely used
Answer: