DYou know what a hotel is, of course. And perhaps, you also know what a condo is a residential（居住的） building divided into separate units that are owned by different people. What you may not know is that in some U.S. cities, the two have come together into something called a "condo hotel".Some condo hotels can now be found in beach and mountain towns and a few small cities. However, none is more famous than the great 105-year-old Plaza Hotel in New York, on Fifth Avenue across from Central Park. The Plaza closed for repair in 2005. When it reopened two years later, more than half of it had been changed into one of these modern condo hotels.Here' s how it works : You buy what equals to an apartment （公寓）.If it's at The Plaza, it will cost you between $1.5 million and $9 million. So you own a part of the building. But there's some in convenience. You may stay there no more than 120 days a year. The rest of the time, the hotel's workers can book guests into your place, just as they would in the regular hotel's rooms. So if you' re lucky and rich, you can now live in really special quarters up to almost one third of the year, while others pay off your mortgage （房贷） the rest of the year.So far, a great many of the nation's condo hotel units have been purchased not by rich people but by richer companies, including foreign ones. They want a nice place for their bosses to stay when they're in town or working late at the office.What do we know about a condo hotel?