Which statement is true?

• A. In the 1970s, sheet-metal workers' knowledge of HVAC systems allowed them to move into energy-management positions.
• B. In 1884, William Dunn and Alfred Bowers stamped the first metal airplane wing.
• C. The Pittsburgh machine formed the Pittsburgh seam pocket lock through a series of handbrake bends.
• D. World War I decreased the need for skilled workers in the sheet-metal trade.

Answer: (A)

This option reflects how the sheet-metal trade expanded with building systems and energy awareness. In the 1970s, energy costs rose and energy efficiency became a priority. Sheet-metal workers who understood HVAC systems could design, fabricate, and install ductwork while also contributing to energy management—monitoring performance and helping reduce consumption in buildings. That blend of hands-on ductwork work and system knowledge created opportunities in energy-management roles, making this statement true.

The other ideas don’t align with common trade history. The notion of stamping the first metal airplane wing in 1884 isn’t a well-supported milestone, and the Pittsburgh seam pocket lock described via handbrake bends isn’t a standard, widely taught fact in this trade. World War I generally increased demand for skilled metal workers due to生产 for weapons, ships, and aircraft, rather than decreasing it.