Part 2. Questions 66 – 75

Read the passage below and choose the best answer to each question

    Wood has long been a popular building material in North America because it has generally been plentiful and cheap. Swedish settlers in Delaware built log cabins as early as 1630s. In New England, British colonists built wooden ‘saltbox houses’. Most of the wooden homes of Colonial times could be built with simple tools and minimal skills.

    In the early 19^th century, the standard wooden house was built with beams set into heavy posts and held together with wooden pegs. This method of construction was time – consuming and required highly skilled workers with special tools. The balloon – frame house, invented in 1833 in Chicago by a carpenter from Hartford. Connecticut, used a frame of lightweight lumber, mostly 2´4 and 2´6 inches. This type of house could be assembled by any careful worker who could saw in a straight line and drive a nail.

    This revolution in building was made possible by improved sawmills that could quickly cut boards to standard sizes and the lower cost of lumber that resulted. There were also new machines that could produce huge quantities of inexpensive nails. Skeptics predicted that a strong wind could send such houses flying through the air like balloons and, at first ‘balloon frame’ was a term of derision. But the light frames proved practical, and wooden houses have been basically built this way ever since.

What is the main purpose of the passage?