单选题：Questions are based on the following passage.The reflective

Questions are based on the following passage.
The reflective towers of New York City, which is on the Atlantic migrating (迁徙的)route, can be deadly for birds."We live in an age of glass," said Ms.Laurel, an architect.(76) "It can be a perfect mirror in certain lights, and the larger the glass, the more dangerous it is." About 90,000 birds are killed by flying into building in the city each year.often, they strike the lower levels of glass towers after searching for food in nearby parks.Such crashes are the second-leading
cause of death for migrating birds, after habitat(栖息地) loss, with an estimated number of death ranging up to a billion a year.
(77) As glass office and apartment towers have increased in the last decade, So, too, have calls to make them less deadly to birds.San Francisco adopted bird-safety standard for new building in July.The United States Green Building Council, a nonprofit industry group that encourages the creation of environmentally conscious buildings, will introduce a bird-safety credit this fall as part of its environmental certification process.
There are no easy fixes, however.A few researchers are exploring glass designs that use ultraviolet(紫外线的)signals, but they are still in their infancy.Covers, dot patterns, shades and net are the main options available.
Often, only one section of a building needs to be changed."You don' t necessarily have to treat every window," Ms.Laurel said."It would be too expensive to do the whole building." The Jacob K.Javits Convention Center, which has been undergoing alterations, is the most recent building to voluntarily correct the problem of bird crashes.The architects used less reflective glass and dot patterns.
What is the main idea of the passage? A．New York is a city of glass towers.
B．Glass tower are dangerous for migrating birds.
C．New York adopted new safety standards for buildings.
D．Glass towers are a new trend in the United States.