**Core Concept**
Krukenberg tumors are a type of metastatic cancer that involves the ovaries, typically originating from a primary malignancy in the gastrointestinal tract, particularly the stomach.

**Why the Correct Answer is Right**
Krukenberg tumors are characterized by the presence of mucin-filled signet-ring cells in the ovaries. The primary malignancy in the gastrointestinal tract, especially the stomach, produces tumor cells that invade the lymphatic vessels and ultimately reach the ovaries through hematogenous spread. The stomach cancer cells then implant in the ovarian tissue, leading to the formation of Krukenberg tumors. This process is a classic example of metastasis, where cancer cells from a primary site spread to a distant organ.

**Why Each Wrong Option is Incorrect**

**Option A:** This option is incorrect because Krukenberg tumors are not primary ovarian cancers but rather metastatic deposits from a distant site.
**Option B:** This option is incorrect because while the uterus can be a site for metastasis, it is not the primary source of Krukenberg tumors.
**Option C:** This option is incorrect because the liver is a common site for metastasis from gastrointestinal cancers, but it is not the correct origin of Krukenberg tumors.

**Clinical Pearl / High-Yield Fact**
When diagnosing Krukenberg tumors, it is essential to investigate the primary site of the malignancy, which is often the stomach. A thorough history, physical examination, and imaging studies can help identify the primary tumor site, guiding further management.

**Correct Answer:** D. The stomach.