单选题：Questions are based on the following passage.Cheating in GC

Questions are based on the following passage.
Cheating in GCSE and A-Levels by pupils, teachers and even school exam centres rose markedly last year, with ever more sophisticated electronic gadgets being smuggled into exam halls. The number of teenagers found guilty of cheating rose by 6.2% to 4415 during last summer's exams. But not only pupils were at it--the number of teachers disciplined for test "malpractice" was 30% higher than the year before.
A breakdown of figures from the Office of the Qualifications and Exams Regulator (Ofqual) showed that the most common form of cheating was "bringing a mobile phone or other electronic gadget" into the room. Some candidates were caught with concealed earpieces, described as "exam cheat equipment" on some of the websites that sell them, which could receive information from outside an exam hall. Exam bosses admitted that these were more difficult to detect, although many schools now use mobile tracking devices to detect whether a signal is being sent from any wherein the room. The second most common cause of malpractice was plagiarism (剽窃) or copying other students' work, which accounted for 1084 cases. Disruptive behavior in the exam room, including swearing (讲脏话), rose from 514cases in 2008 to 539 last year. Candidates were also docked marks for including offensive and obscene comments in their exam papers.
In total,2155 students lost marks after being found guilty,644 failed their exams and 1616.escaped with warnings. "Candidates who bring a mobile phone into an exam room but do not have the phone at their desk might receive a warning, whereas candidates found using a mobile phone during an exam might be disqualified from the unit or qualification in the current exam series," a spokesman for Ofqual explained.
The number of teachers disciplined rose from 68 to 88, and 17 were suspended from invigilating in exams. Their crimes include leaving the exam hall unsupervised and helping candidates to answer questions.
Ofqual stressed that the figures confirmed that only 0.03% of pupils cheated in exams taken last summer. However, Jim Sinclair, director of the Joint Council for Qualifications, the organization which represents the examination boards, said it took a "zero tolerance" approach to all forms of cheating, including the possession of unauthorized items such as mobile phones, iPods and other digital music players.
Mick Brookes, of the National Association of Head Teachers, said he did not condone cheating but pointed out that children knew some exams were "extremely high stakes" and schools were under more pressure to succeed. "Young people are in a highly pressurized environment, partly due to the jobs market being more difficult than it was, and university entrance being restricted," he added.
According to exam bosses, what have schools done to tackle high-tech cheating? A．Conceal the equipment students commonly use.
B．Block the websites selling these equipment.
C．Employ mobile tracking devices to detect signals.
D．Cut off mobile signals outside the exam hall.