根据以下资料，回答下列各题： One of the many pleasures of watching Mad Men，a television drama about the advertising industry in the early 1960s，is examining the ways in which office life has changed over the years．One obvious change makes people feel good about themselves：they no longer treat women as second—class citizens．But the other obvious change makes them feel a bit more uneasy：they have lost the art of enjoying themselves at work． The ad—men in those days eaioyed simple pleasures．They puffed away at their desks．They drank throughout the day．They had affairs with their colleagues．They socialised not in order to bond，but in order to get drunk．Nowadays many companies are obsessed with fun． Software firms in Silicon Valley have installed rock—climbing walls in their reception areas and put inflatable animals in their offices．Wal-Mart orders its cashiers to smile at all and sundry． The cult of fun has spread like some disgusting haemorrhagic disease． This cult of fun is driven by three of the most popular management fads of the moment： empowerment．engagement and creativity．Many companies pride themselves on devolving power to front-line workers．But surveys show that only 20％of workers are“fully engaged with their．iob”．Even fewer are creative．Managers hope that“fun”will magically make workers more engaged and creative．But the problem is that as soon as fun becomes part of a corporate strategy it ceases to be fun and becomes its opposite-at best an empty shell and at worst a tiresome imposition． The most unpleasant thing about the fashion for fun is that it is mixed with a large dose of Dressure．Boston Pizza encourages workers to send“golden bananas”to colleagues who are“having fun while being the best”．Behind the“fun”there often lurks some crude management thinking：a desire to brand the company as better than its rivals，or a plan to boost productivity through team．building．Twitter even boasts that it has“worked hard to create an environment that spawns productMty and happiness”． While imposing fake fun on their employees，companies are battling against the real thing．Many force smokers to huddle outside like furtive criminals．Few allow their employees to drink at lunch time，let alone earlier in the day．A regiment of busybodies--from lawyers to human resources functionaries-is waging war on office romance，particularly between people of different ranks． The merchants of fake fun have met some resistance．When Wal—Mart tried to impose alien rules on its German staff-such as compulsory smiling and a ban on affairs with co-workers—it touched off a guerrilla war that ended only when the supermarket chain announced it was pulling out of Germany in 2006．But such victories are rare．For most wage slaves forced to pretend they are having fun at work，the only relief is to poke fun at their tormentors．Mad Men reminds people of a world they have lost—a world where bosses did not think that“fun”was a management tool and where employees could happily quaff Scotch at noon．Cheers to that． In the opening paragraph，the author introduces his topic by_____.
A.explaining a phenomenon
B.justifying an assumption
C.posing an argument
D.making a contrast