单选题   Para. 1 'Do not write on the walls,' reads the message on a Renaissance stone wall in the cathedral on Florence's central square.
    Para. 2 Unfortunately, the instruction, scrawled in black marker, was the defiant graffiti of a visitor who had decided to mock the plastic sign just above it by saying the same thing.
    Para. 3 The official missive, on a wall at the end of a steep staircase leading up to the dome of the Santa Maria del Fiore cathedral, better known as the Duomo, had clearly failed in its mission.
    Para. 4 ①For years, officials in Florence have tried to discourage visitors from around the world from using this city's old stone walls as a time capsule for such musings. ②But the human urge to generate graffiti, it seems, is a powerful instinct, difficult to tame.
    Para. 5 So the officials have decided to try a digital solution to their age-old problem, starting with Giotto's bell tower, the Campanile.
    Para. 6 Having finally cleaned up all the walls along the 414-step climb to the bell tower earlier this year, officials have placed three tablets there, hoping visitors will leave their marks, virtually, without damaging the monument itself.
    Para. 7 Messages will be stored on a website and archived, for eternity, online.
    Para. 8 Any other mark will be removed swiftly, a large billboard at the entrance of the bell tower explains in both Italian and English.
    Para. 9 'We needed something to act as a deterrent against new graffiti, once all the walls were clean, and we hope that this app will do that,' said Alice Filipponi, the social media strategist at an institution that oversees Florence's Duomo complex.
    Para. 10 'Our goal was to let people leave their testimony without smearing the walls again,' Filipponi said.
    Para. 11 In the first three days of their experiment, there were more than 3,000 visitors, 304 digital messages—and no new graffiti scrawls.
    Para. 12 ①With virtual graffiti, visitors can select the background they want to write on: wood or marble, iron or plaster—like that found in the monument. ②Then, with their tool of choice, from lipstick to spray paint, they are able to use their fingertips to etch symbols, names and messages.
    Para. 13 ①'Whether we manage to educate people remains to be seen,' said the institution's president, Franco Lucchesi. ②'But as of now, our Internet is full of messages, and the walls are not. ③We call therefore say that it's working.'
    Para. 14 ①Some have confessed to their misdeeds ②Lucchesi recalls the 'pilgrimages' of a Japanese class coming to apologize for the damage done by students—three years in a row.
    Para. 15 ①'The fact that the monument is so clean also helps,' said Laura Bachmann, a 21-year-old from Germany who was visiting Florence with a friend. ②'None dares to be the first one to dirty it up.'
    Para. 16 ①To the experts, that cleanness is the main deterrent. ②'Vandals do it where everyone can see their mark. ③Unfortunately, I fear it's not a tablet that can prevent recidivism.' Andrea Amato, president of Italy's National Anti-Graffiti Association, said about the effort in Florence. ④'Entire walls available for graffiti writers have not impeded them to dirty up elsewhere.'
    Para. 17 ①He added: 'But it's important that we don't abandon our monuments to degradation. ②If we clean them, it's psychologically harder for people to smear them up again.'