A.I. Explanation:

Option 1: "The construction of artificial dams"

Explanation: This option is incorrect because the text does not mention artificial dams as a factor in the formation of waterfalls. The focus is on natural processes, specifically erosion, rather than human-made structures.

Option 2: "The differential erosion of underlying riverbeds"

Explanation: This option is correct as the text explicitly states that the steep gradient of the waterfall results from the differential erosion of the underlying riverbed. It describes how the river encounters different types of rock, leading to varying rates of erosion, which creates the waterfall.

Option 3: "Sudden geological shifts or earthquakes"

Explanation: This option is incorrect because the text does not mention geological shifts or earthquakes as causes for waterfall formation. Instead, it emphasizes the gradual process of erosion over time.

Option 4: "The accumulation of large amounts of rainfall"

Explanation: This option is incorrect as the text does not attribute the formation of waterfalls to rainfall accumulation. The focus is on the erosion process rather than precipitation.