If water is the primary transport mechanism for a given sediment, the grain size MOST closely indicates the: a. geographic extent of the weathering source rock at outcrop.
b. average velocity of the water from the time of erosion until deposition.
c. velocity of the water at the moment the sediment settled to the bottom.
d. climate conditions at the time of deposition

c. velocity of the water at the moment the sediment settled to the bottom.

Explanation:

The size of a grain determines the speed with which a stream of water will be able to transport that grain to the bottom of a system. This is because the grain size is directly related to its mass. This causes larger grains to be transported at a slower speed, as they make it harder for water to carry them, due to their weight. On the other hand, smaller grains are lighter and offer less water resistance, being carried more easily.