Answer:

The correct answer is D. wind.

Explanation:

When sun dunes are deposited, it is primarily due to the action of wind. Wind carries and transports loose sediment particles, such as sand, and deposits them in the form of dunes. The wind's force and direction play a significant role in shaping and moving these dunes over time. As the wind blows, it picks up sand particles from exposed surfaces and transports them to areas of lower wind velocity or obstruction, resulting in the formation and deposition of sand dunes. Therefore, wind is the primary agent responsible for the deposition of sand dunes.