Question

1. why do sand dunes form?wind carrying sand grains crosses a depression and deposits the sand.wind carries sand grains, which hit an obstacle and collect in one place.wind picks up the sand and carries it away from the area.wind carrying sand grains speeds up and deposits the sand grains.

Explanation:

Sand dunes form when wind-transported sand grains encounter an obstacle (like a rock, plant, or even a small change in terrain). The obstacle slows the wind, reducing its ability to carry sand, so the sand drops and accumulates over time, building up into a dune. The other options are incorrect: wind crossing a depression does not directly cause dune formation, just moving sand away only causes erosion, and faster wind carries more sand rather than depositing it.

Answer:

Wind carries sand grains, which hit an obstacle and collect in one place.