Which unusual sign has historically been associated with an economic boom nearing its peak?

Answer: C Record-breaking skyscrapers being built.

Explanation: It’s known as the Skyscraper Index.

The idea, popularised by property analyst Andrew Lawrence in 1999, is that plans for record-breaking buildings tend to emerge during periods of abundant credit, soaring property values and extreme confidence — precisely the conditions that can accompany the final stages of a boom.

Famous examples include New York’s skyscraper race around the 1929 crash and the Burj Khalifa, conceived during Dubai’s boom before the global financial crisis.