Question

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:

The text states the area was first a flowing river, then dried to a desert with wind-deposited sediment. Rivers deposit larger particles (pebbles + sand) due to water flow, while wind in deserts deposits finer sand. So the order is river deposits (sand/pebbles) first, then wind deposits (sand) later.

Answer:

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