How are coastal dunes and coastal plains similar?

Coastal dunes are a ridge, or a series of ridges, that form at the rear of a beach and differ from most other constructional coastal landforms in that they are formed by the movement of air (aeolian transport) rather than by tidal, wave, or current action.A coastal plain is a flat, low-lying piece of land next to the ocean. Coastal plains are separated from the rest of the interior by nearby landforms, such as mountains. In western South America, a large coastal plain lies between the Andes Mountains and the Pacific Ocean.

Explanation:

the answer would be b).