**Core Concept**
The formation of bladder stones is often related to **urinary stasis**, **infection**, and **metabolic disorders**. Bladder stones can be composed of various materials, including calcium oxalate, uric acid, and magnesium ammonium phosphate.

**Why the Correct Answer is Right**
The most common type of bladder stone is typically composed of **uric acid** or **calcium oxalate**, but in many cases, especially in developing countries, the commonest bladder stone is actually a **uric acid stone** due to factors like low fluid intake and dietary habits.

**Why Each Wrong Option is Incorrect**
**Option A:** This option might be incorrect because, although calcium oxalate stones are common in the kidney, they are not the most common in the bladder.
**Option B:** Without the specific details of this option, it's hard to provide a precise reason, but generally, other types of stones like cystine or xanthine are less common than uric acid stones in the bladder.
**Option D:** Similarly, without specifics, if this option refers to another type of stone, it would be less common than uric acid stones in the context of bladder stones.

**Clinical Pearl / High-Yield Fact**
It's crucial to remember that the composition of bladder stones can vary significantly based on geographical location, dietary habits, and the presence of underlying medical conditions. Uric acid stones are more radiolucent and thus may not show up as clearly on plain X-rays compared to calcium-based stones.

**Correct Answer:** Correct Answer: D. Uric acid stone.