18.
the most prominent features of a narrow, v-shaped valley, where the stream profile drops rapidly, are

meanders and floodplains
rapids and waterfalls
lakes and ponds
deltas and natural levees 18.
the most prominent features of a narrow, v-shaped valley, where the stream profile drops rapidly, are

meanders and floodplains
rapids and waterfalls
lakes and ponds
deltas and natural levees

The correct answer is rapids and waterfalls.  

Rapids refers to the segments of streams with extensively vigorous currents, various obstacles, and steps in their streambeds. A waterfall refers to a vertical drop in a stream bed. Both are the locations of vigorous erosion.  

The rapids are generally produced where the resilient bedrock limits a stream to a narrow channel and forces an enhancement in the velocity of water.  

On the other hand, waterfalls are produced where the fast-flowing water negotiates a geologic contact amid the more resilient and less resistant layers of rock, or through a fault, which has analogized distinct kinds of rocks. Or it can be said that waterfalls usually produce at the end of a series of rapids.  

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