**Core Concept**
Mandibular reconstruction often requires a graft that can withstand the mechanical stress and masticatory forces in the oral cavity. The ideal graft should be durable, have sufficient bone volume, and be easily harvested with minimal donor site morbidity.

**Why the Correct Answer is Right**
The most preferable graft for mandibular reconstruction is a fibula flap. This is because the fibula bone is long, thin, and cylindrical, allowing it to be easily shaped and contoured to match the recipient site. Additionally, the fibula has a robust blood supply, making it less prone to complications such as bone necrosis. The fibula flap also has a significant amount of soft tissue, including skin and muscle, which can be used for reconstruction of the overlying soft tissue.

**Why Each Wrong Option is Incorrect**
**Option A:** The iliac crest graft is not ideal for mandibular reconstruction due to its limited length and thickness, making it difficult to shape and contour to match the recipient site.
**Option B:** The scapular graft is not suitable for mandibular reconstruction because it often requires a second donor site, and the bone is not as strong as the fibula.
**Option C:** The radius graft is not a good option for mandibular reconstruction due to its limited size and the risk of complications such as bone necrosis.

**Clinical Pearl / High-Yield Fact**
When considering graft options for mandibular reconstruction, it's essential to evaluate the patient's overall oral and maxillofacial anatomy, as well as their medical history and comorbidities, to determine the most suitable graft for their specific needs.

**Correct Answer: D. Fibula flap.**