5. Read the text and fill in the gaps transforming the capitalized words.

History of Skyscrapers

Two (1) discoveries in the middle of the 1800s made it possible to build modern skyscrapers. Before the Revolution brick and stone walls carried the industry of buildings. Because each floor was very heavy it was impossible to build very high houses. In possible the middle of the 19th century steel became an important (5) material. This metal was strong and build light. Architects could now construct a steel skeleton to support very tall (6) buildings. Chicago's Home Insur- buildance Company Building was ten-stories tall and the first skyscraper to use such a steel (7) construction. Skyscrapers would have been (8) difficult if people had to use walk up and down many flights of stairs. In 1853 an (9) elevator safe enough to carry passengers was invented by Elisha Graves Otis. (To be continued)