**Core Concept**
The question is testing the understanding of the classification of injuries in the context of forensic medicine. In forensic medicine, injuries are categorized based on their cause and timing of occurrence. Understanding these categories is crucial for investigators to reconstruct the sequence of events surrounding a crime or accident.

**Why the Correct Answer is Right**
The correct answer is **Secondary injury**. A secondary injury occurs when a person strikes an object after being thrown or propelled by a primary force, such as a vehicle. This type of injury is caused by the person's body hitting an object, like a tree, wall, or pavement, resulting in additional trauma. The mechanism of secondary injury involves the transfer of kinetic energy from the primary force to the object, causing further damage to the body.

**Why Each Wrong Option is Incorrect**
**Option A:** **Primary injury** refers to the initial injury caused by the primary force, such as a vehicle collision. It is not the injury caused by striking an object on the road.
**Option C:** **Acceleration injury** occurs when a person's body is rapidly accelerated, such as in a vehicle crash. This is not the same as striking an object on the road.
**Option D:** **Deceleration injury** occurs when a person's body is rapidly decelerated, such as in a vehicle crash. This is also not the same as striking an object on the road.

**Clinical Pearl / High-Yield Fact**
In forensic medicine, it's essential to distinguish between primary and secondary injuries to accurately reconstruct the sequence of events surrounding an accident or crime. This can be a crucial factor in determining liability and assigning blame.

✓ Correct Answer: B. Secondary injury