Question

sediment deposited by a fast-flowing river
over thousands of years, the river dried up, and the area became a desert. in the desert, sediment was deposited by wind.
sediment deposited in a desert
how did the sediment deposited in this area change over time?
first, a layer of sand and pebbles was deposited. later, a layer of sand was deposited.
first, a layer of sand was deposited. later, a layer of sand and pebbles was deposited.

Explanation:

Fast-flowing rivers deposit larger particles like pebbles with sand. When the area became a desert, wind (a weaker agent) deposits only smaller sand particles. So the order is first sand and pebbles, then sand.

Answer:

First, a layer of sand and pebbles was deposited. Later, a layer of sand was deposited.