## **Core Concept**
The question tests knowledge of the histological structure of various parts of the gastrointestinal tract, specifically focusing on the composition of the wall of certain organs. The gastrointestinal tract is primarily composed of four layers: mucosa, submucosa, muscularis externa, and serosa or adventitia. The muscularis externa can be either **smooth muscle** (in the esophagus, stomach, small intestine, and large intestine) or **striated muscle** (in the pharynx and the upper part of the esophagus).

## **Why the Correct Answer is Right**
The correct answer, **D. Gallbladder**, has a wall composed of **fibromuscular** tissue. The gallbladder wall consists of a mucosa, a **fibromuscular** layer (which is actually a layer of smooth muscle and fibrous tissue), and a serosa. This fibromuscular layer provides the gallbladder with its ability to contract and release bile into the bile duct.

## **Why Each Wrong Option is Incorrect**
- **Option A:** The esophagus primarily has a **muscularis externa** composed of **striated muscle** in the upper part and **smooth muscle** in the lower part, not fibromuscular in the traditional sense of being specifically described as such for its entire wall composition.
- **Option B:** The stomach wall is composed of mucosa, submucosa, **muscularis externa** (with inner circular and outer longitudinal layers of smooth muscle), and serosa. It does not have a fibromuscular wall.
- **Option C:** The small intestine wall includes mucosa, submucosa, **muscularis externa** (with inner circular and outer longitudinal layers of smooth muscle), and serosa. Like the stomach, it does not have a fibromuscular wall.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the **gallbladder** can be surgically removed (cholecystectomy) if it becomes diseased, such as in cholecystitis or due to gallstones. After cholecystectomy, the body compensates by dilating the bile ducts to store bile.

## **Correct Answer:** D. Gallbladder.