Which statement is true?

• A. In 1884, William Dunn and Alfred Bowers stamped the first metal airplane wing.
• B. The Pittsburgh machine formed the Pittsburgh seam pocket lock through a series of handbrake bends.
• C. World War I decreased the need for skilled workers in the sheet-metal trade.
• D. Tin plate was produced on a large scale in the United States in 1878.

Answer: (D)

The idea being tested is how the sheet-metal industry evolved in the late 19th century, particularly the development of tin plate production in the United States. Tin plate—steel coated with tin—was essential for cans and many durable metal goods, and its production scaled up as demand from the booming canning industry grew.

That statement is the best because, by around 1878, U.S. mills had begun producing tin plate on a large scale to support domestic canning and consumer packaging. This reflects a key moment in the shift from craft to mass production in the sheet-metal trades, enabling widespread use of tin-coated steel in everyday products.

The other options don’t fit the timeline: metal airplane wings weren’t stamped in 1884; the specific “Pittsburgh seam pocket lock” process isn’t a recognized early hallmark of the trade; World War I actually increased the demand for skilled sheet-metal workers rather than reducing it.