**Core Concept**
The question requires understanding of **trauma** and **injury patterns**. Extensive abrasions all over the body suggest a high-energy impact, likely from a **vehicle collision**.

**Why the Correct Answer is Right**
Given the context of a pedestrian found by the roadside with extensive abrasions, the most plausible explanation is a **road traffic accident**. The mechanism of injury in such cases often involves the pedestrian being struck by a vehicle, resulting in **friction burns** or **abrasions** as the body scrapes against the road surface.

**Why Each Wrong Option is Incorrect**
**Option A:** Not provided, so assuming it's an unrelated cause.
**Option B:** Not provided, so assuming it's an unrelated cause.
**Option C:** Not provided, so assuming it's an unrelated cause.
**Option D:** Not provided, but likely an incorrect explanation for the injuries.

**Clinical Pearl / High-Yield Fact**
In cases of pedestrians hit by vehicles, **patterned abrasions** can indicate the direction of the impact and the type of vehicle involved. Always consider **road traffic accident** in pedestrians found injured by the roadside.

**Correct Answer:** D. Road traffic accident.