Reading comprehension It happens to every medical student sooner or later. You get a cough that persists for a while. Ordinarily,you would just ignore it--but now, armed with your rapidly growing medical knowledge, you can’t help worrying. The cough could mean just a cold, but it could also be a sign of lung cancer.　　For doctors in training, nurses and medical journalists, hypochondria is an occupational danger. The feeling usually passes after a while, leaving only a funny story to tell at a dinner party. But for the tens ofthousands who suffer from true hypochondria they live in constant terror that they are dying of some awfuldisease, or even several awful diseases at once. Doctors can assure them that there’s nothing wrong, but since the cough is real, the assurances fall on deaf ears. And because no physician or test can offer a 100% guarantee that one doesn’t have cancer, a hypochondriac always has fuel to feed Iris .or her worst fears.　　Hypochondriacs don’t harm just themselves; they block the whole healthcare system. Although they account for only about 6% of the patients who visit doctors every year, they tend to burden their physicians with frequent visits that take up excessive amounts of time. And the problem may be worse, thanks to the popularity of medical information on the Internet. They go on the Web and learn about new diseases and new presentations of old diseases that they never even knew about before. Doctors have taken to calling this phenomenon cyberchondria (网络疑病症).Choose correct answers to the question:Why can’t doctors convince the suffers that there is nothing wrong?
选项：

A:Because the doctors can’t cure the minor diseases.;
B:Because the doctors don’t assure them of that.;
C:Because the sufferers are deaf and cannot hear what the doctors say.;
D:Because lack of absolute guarantee makes the patients doubtful.