Builder: Within ten years, most of the new homes constructed in North America will have steel frameworks rather than wood ones. After all, two-by-fours and two-by-sixes -- the sizes of lumber most commonly used in home construction -- are deteriorating in quality and increasing in cost, while environment-friendly steel is decreasing in cost. In addition, unlike wood, steel will not warp, rot, or split. Which one of the following, if true, most seriously weakens the builder's reasoning? ['Training home construction workers to work with steel is very costly.', 'Steel-framed homes do not have to be treated with pesticides or other chemicals that can contribute to indoor air pollution.', 'Because lumber prices have increased over the last decade, currently most new homes are built with steel frameworks.', 'The number of houses built each year is expected to decrease over the next decade.']