**Core Concept**
The question is testing the student's understanding of the muscles involved in maintaining the position of the tongue, particularly in the context of a mandibulectomy, where the lower jawbone is surgically removed. The primary muscle responsible for preventing the tongue from falling back is a key concept in oral and maxillofacial surgery.

**Why the Correct Answer is Right**
The hyoglossus muscle plays a crucial role in depressing and retracting the tongue, which helps to prevent it from falling back into the pharynx. This muscle originates from the hyoid bone and inserts into the lateral surface of the tongue, allowing for precise control over tongue movement. In the absence of the mandible, the hyoglossus muscle becomes even more critical in maintaining the position of the tongue.

**Why Each Wrong Option is Incorrect**
**Option A:** The genioglossus muscle is the primary muscle responsible for protruding the tongue, not preventing it from falling back. While it does play a role in maintaining the position of the tongue, it is not the primary muscle in this context.

**Option C:** The palatopharyngeus muscle is involved in swallowing and the elevation of the larynx, but it is not directly responsible for preventing the tongue from falling back.

**Option D:** This option is incorrect because only one muscle is primarily responsible for preventing the tongue from falling back.

**Clinical Pearl / High-Yield Fact**
In the event of a mandibulectomy, the hyoglossus muscle is crucial for maintaining the position of the tongue, and its function should be carefully assessed during postoperative care to prevent complications such as dysphagia or respiratory distress.

**✓ Correct Answer: B. Hyoglossus**