**Core Concept**
The question is testing the ability to identify an isotope that selectively accumulates in abscess cavities, which is a key concept in nuclear medicine. This involves understanding the properties of various isotopes and their behavior in different pathological conditions.

**Why the Correct Answer is Right**
The correct answer is Technetium-99m sulfur colloid. This is because Technetium-99m sulfur colloid is taken up by the reticuloendothelial system (RES), which includes macrophages that accumulate in abscess cavities. This leads to selective concentration of the isotope in the abscess, making it useful for imaging purposes.

**Why Each Wrong Option is Incorrect**
**Option A:** Technetium-99m pertechnetate is incorrect because it is primarily taken up by the thyroid gland and not by the RES.

**Option B:** Gallium-67 citrate is incorrect because it is primarily taken up by inflammatory cells and not specifically by macrophages in abscess cavities.

**Option C:** Indium-111 oxine is incorrect because it is primarily taken up by leukocytes and not specifically by macrophages in abscess cavities.

**Clinical Pearl / High-Yield Fact**
Technetium-99m sulfur colloid is a commonly used radiopharmaceutical for imaging the RES and detecting abscesses, but it should be used with caution in patients with liver disease, as it can accumulate in the liver and cause false-positive results.

**Correct Answer:** D. Technetium-99m sulfur colloid