**Core Concept**
The question is testing the understanding of the histopathological criteria for assessing the risk of malignancy in endometrial polyps. Endometrial polyps are growths in the lining of the uterus (endometrium) that can be benign or malignant. The risk of malignancy is evaluated based on the histopathological features of the polyps.

**Why the Correct Answer is Right**
Complex hyperplasia with atypia represents a high-grade lesion characterized by an increased number of cells, abnormal cell growth, and the presence of atypical cells. The presence of atypia indicates a high risk of malignancy due to the likelihood of genetic mutations and uncontrolled cell division. The complex hyperplasia component further increases the risk due to the presence of multiple layers of cells and abnormal glandular architecture. This combination of features is associated with a higher likelihood of progression to endometrial carcinoma.

**Why Each Wrong Option is Incorrect**
**Option A:** Simple hyperplasia with atypia does not necessarily indicate a high risk of malignancy. While the presence of atypia is concerning, the simple hyperplasia component suggests a lower grade lesion with less risk of progression to cancer.

**Option B:** Simple hyperplasia without atypia is generally considered a low-grade lesion with a low risk of malignancy. The absence of atypia and the simple hyperplasia component suggest a benign growth with little potential for progression to cancer.

**Option D:** Complex hyperplasia without atypia is a more concerning lesion than simple hyperplasia, but the absence of atypia reduces the risk of malignancy. This option is still considered a high-grade lesion, but the risk of cancer is lower than in complex hyperplasia with atypia.

**Clinical Pearl / High-Yield Fact**
When evaluating the risk of malignancy in endometrial polyps, it's essential to consider both the histopathological features and the clinical context. Complex hyperplasia with atypia is a red flag for endometrial cancer, and patients with this diagnosis should undergo further evaluation and follow-up.

**✓ Correct Answer: C. Complex hyperplasia with atypia**