Concept:A wadi is a steep-sided, flat-floored desert valley that carries water only during occasional flash floods.
Explanation:In hot deserts, valleys often remain dry for long periods.
A wadi is shaped by rare but intense rainfall, when flash floods rush through the valley.
Its sides are steep, while its floor is wide and flat, formed by the movement of flood water.
This matches the description in the question exactly.
The other options do not fit the definition.
A bajada is a sloping deposit of rock debris at the base of a desert mountain.
A headland is a coastal landform, not a desert valley.
A playa is a dry lake bed in a desert basin, not a valley through which floods flow.
Therefore, the correct answer is wadi.
Answer:D. wadi