Read the following passage and mark the letter A, B, C, or D to indicate the correct answer to each of the questions from 30 to 34  

     Central Park, emerging from a period of abuse and neglect, remains one of the most popular attractions in New York City, with half a million out-of-towners among the more than 3 million people who visit the park yearly. About 15 million individual visits are made each year.  

     Summer is the season for softball, concerts, and Shakespeare; fall is stunning; winter is wonderful for sledding, skating, and skiing; and springtime is the loveliest of all. It was all planned that way. 

     About 130 years ago Frederic Law Olmsted and his collaborator Calvert Vaux submitted their landscaping plan for a rectangular parcel two miles north of the town's center. The barren swampy tract, home for squatters and a bone-boiling works that made glue, was reported as “a pestilential spot where miasmic odors taint every breath of air." It took 16 years for workers with pickaxes and shovels to move 5 million cubic feet of earth and rock, and to plant half a million trees and shrubs, making a tribute to nature-a romantic nineteenth-century perception of nature.  

     What exists today is essentially Olmsted and Vaux's plan. with more trees, buildings, and asphalt.  Landscape architects still speak reverently of Olmsted's genius and foresight, and the sensitive visitor can see the effects he sought.  

With what subject is the passage mainly concerned?