题目内容：
Questions are based on the following passage．Most of us experience false alarms with phones, because it is a common andunavoidable part of healthy brain function.
Sensing phantom ( 错觉的 ) phone vibrations is a strangely common experience.
Around 80% of us have imagined a phone vibrating in our pockets when it's actuallycompletely still. Almost 30% of us have also heard non-existent ringing. Are thesehallucinations ( 幻觉 ) ominous ( 不详的 ) signs of impending madness caused bydigital culture?
Not at all. In fact, phantom vibrations and ringing illustrate a fundamental principlein psychology.
It's an example of a perceptual system, just like a fire alarm, an automatic door, ora daffodil bulb that must decide when spring has truly started. Your brain has to makea perceptual judgment about whether the phone in your pocket is really vibrating. And,analogous to a daffodil bulb on a warm February morning, it has to decide whether theincoming signals from the skin near your pocket indicate a true change in the world.
Psychologists use a concept called Signal Detection Theory to guide their thinkingabout the problem of perceptual judgments. Analyzing the example of phone vibrations,we can see how this theory explains why they are a common and unavoidable part ofhealthy mental function.
When your phone is in your pocket, the world is in one of two possible states: thephone is either tinging or not. You also have two possible states of mind: the judgmentthat the phone is tinging, or the judgment that it isn't. Obviously you'd like to match thesestates in the correct way. True vibrations should go with "it's ringing", and no vibrationsshould go with "it's not ringing". Signal detection theory calls these faithful matches a "hit"and a "correct rejection", respectively.
But there are two other possible combinations: you could mismatch tree vibrationswith "it's not ringing" (a "miss"); or mismatch the absence of vibrations with "it's tinging"(a "false alarm"). This second kind of mismatch is what's going on when you imagine aphantom phone vibration.
For situations where easy judgments can be made, such as deciding if someone saysyour name in a quiet room, you will probably make perfect matches every time. But whenjudgments are more difficult--if you have to decide whether someone says your namein a noisy room, or have to evaluate something you're not skilled at--mismatches willoccasionally happen. And these mistakes will be either misses or false alarms.
The experience of sensing phantom phone vibrations is __________. A．an avoidable problem of brain function
B．a common brain problem
C．a sign of impending madness
D．a normal brain function
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