单选题：根据下列材料，回答题A Phone That Knows You're Busy　　It's a modem prob

根据下列材料，回答题 A Phone That Knows You're Busy 　　It's a modem problem: you're too busy to be disturbed by incessant (连续不断的) phone calls so you turn your cell phone off．But if you don't remember to turn it back on when you're less busy. You could miss some important calls if only the phone knew when it was wise to interrupt you, you wouldn't have to turn it off at all. Instead, it could let calls through when you are not too busy.
　　A bunch of behavior sensors (传感器) and a clever piece of software could do just that, by analyzing your behavior to determine if it's a good time to interrupt you. If built into a phone, the system may decide you're too busy and ask the caller to leave a message or ring back later.
　　James Fogarty and Scott Hudson at Camegie Mellon University in Pennsylvania based their system oil tiny microphones, cameras and touch sensors that reveal body language and activity. First they had to study different behaviors to find out which ones strongly predict whether your mind is interrupted.
The potential "busyness" signals they focused on included whether the office doors were left open or closed, the time of day, if other people were with the person in question, how close they were to each other, and whether or not the computer was in use.
　　The sensors monitored these and many other factors while four subjects were at work. At random intervals, the subjects rated how interruptible they were on a scale ranging from "highly interruptible" to "highly not-interruptible". Their ratings were then correlated with the various behaviors . "It is a shotgun (随意的) approach: we used all the indicators we could think of and then let statistics find out which were important, " says Hudson.
The model showed that using the keyboard, and talking on a landline or to someone else in the office correlated most strongly with how interruptible the 　　subjects judged themselves to be. Interestingly, the computer was actually better than people at predicting when someone was too busy to be interrupted．The computer got it right 82 per cent of the time, humans 77 per cent. Fogarty speculates that this might be because people doing the interrupting are inevitably biased towards delivering their message, whereas computers don't care.
　　The first application for Hudson and Fogarty's system is likely to be in an instant messaging system, followed by office phones and cellphones. "There is no technological roadblock (障碍) to it being deployed in a couple of years, " says Hudson.

A big problem facing people today is that________. A．they must tolerate phone disturbances or miss important calls.
B．they must turn off their phones to keep their homes quiet.
C．they have to switch from a desktop phone to a cell phone.
D．they are too busy to make phone calls.