Which area of rivers and streams will most likely contain the most sediment?
a. the source
b. the mouth
c. the middle portion
d. none of the above

The correct answer is - b. the mouth.

The area of the rivers and streams that contains the most sediments is the mouth. The mouth of the rivers and streams is the final part of their flow, and that is the place where most of the sediments that have be taken and carried along the way are starting to deposit, as the speed of the water is getting smaller. Also, this is the part where the rivers and the streams are the biggest, so it simply pure logic that most of the sediments are in the biggest part to which all the faster water from the upper part is bringing everything down to it.

the answer would be b).