The paragraph is followed by an incomplete phrase or sentence which summarizes the main idea of the paragraph. Choose the missing words of the phrase or sentence. 

Many centuries of rain caused huge rivers to move violently through this area. Over time, these rivers cut deep into the new mountains. During the great Ice Age, millions of tons of ice cut and shaped the cooled granite to form giant rocks, known as Half Dome.

Various forms of water （） the outlook of the area.