Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42.Pittsburgh, Pennsylvania, is located where the Allegheny and Monongahela rivers unite to form the Ohio River. Its fascinating history began in 1758 when General John Forbes and his British and colonial army captured Fort Duquesne from the French and renamed it Fort Pitt, for the British statesman William Pitt the Elder. After an agreement between ...

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42.

Pittsburgh, Pennsylvania, is located where the Allegheny and Monongahela rivers unite to form the Ohio River. Its fascinating history began in 1758 when General John Forbes and his British and colonial army captured Fort Duquesne from the French and renamed it Fort Pitt, for the British statesman William Pitt the Elder. After an agreement between the Native American tribes and William Penn's family, settlers henan arrivinn Pittsburah was laid out (1764) by John Campbell in the area around the fort.

Following the American Revolution, the town became an outfitting point for settlers traveling westward down the Ohio River. Pittsburgh's strategic location and wealth of natural resources spurred its commercial and industrial growth in the nineteenth century. A blast furnace, erected by George Anschutz about 1792, was the forerunner of the iron and steel industry that for more than a century was the city's economic power. By 1850, it was known as the "Iron City". The Pennsylvania Canal and the Portage Railroad, both completed in 1834, opened vital markets for trade and shipping.

After the American Civil War, great numbers of European immigrants swelled Pittsburgh's population, and industrial magnates such as Andrew Carnegie, Henry Clay Frick, and Thomas Mellon built their steel empires there. The city became the focus of historic friction between labor and management, and the American Federation of Labor was organized there in 1881. By 1900, the city's population had reached 321,616. Growth continued nearly unabated through World War II, and during the war years, Pittsburgh was a boom town.

During this period of economic and population growth, Pittsburgh became a grimy, polluted industrial city. After the war, however, the city undertook an extensive redevelopment program, with emphasis on smoke-pollution control, flood prevention, and sewage disposal.

In 1957, it became the first American city to generate electricity by nuclear power. By the late 1970s and early 80s, the steel industry had virtually disappeared, but Pittsburgh successfully diversified its economy through more emphasis on light industries and on such high-technology industries as computer software, industrial automation (robotic), and biomedical and environmental technologies.

Which of the following phrases is closest in meaning to the phrase "focus of historic friction" in the passage?