**Core Concept**
Elli's classification is used to describe the severity of injuries to teeth, particularly in the context of dental trauma. It categorizes injuries based on the extent of damage to the tooth structure. Understanding this classification is crucial for dental professionals to assess and manage tooth injuries effectively.

**Why the Correct Answer is Right**
A class IV injury in Elli's classification represents a severe injury where the tooth is fractured, exposing the pulp. This type of injury involves significant damage to the tooth structure, necessitating immediate dental attention to prevent further complications such as infection or tooth loss.

**Why Each Wrong Option is Incorrect**
**Option A:** This option does not accurately represent a class IV injury, as it does not involve exposure of the pulp.
**Option B:** Similarly, this option is incorrect as it does not align with the definition of a class IV injury in Elli's classification.
**Option C:** This option is also incorrect, as it does not match the criteria for a class IV injury.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that prompt treatment of dental injuries, especially those involving pulp exposure, is critical to prevent infection and ensure the best possible outcome for the tooth.

**Correct Answer:** D. Tooth fractured, exposing the pulp.