Direction: In the following passage, some words have been deleted. Fill in the blanks with the help of the alternatives given. Select the most appropriate option for each blank.

Waterfalls are characterized by great (1)______ power. The (2)______ of erosion depends on the height of a given waterfall, its volume of flow, the type and structure of the rocks involved, and other factors. In some cases, the site of the waterfall (3)_______ upstream by headward erosion of the cliff or scarp, (4)______ in others erosion tends to act downward to (5)______ the entire reach of the river containing the falls.