**Core Concept**
The investigation of choice in a postmenopausal woman with bleeding involves evaluating the endometrium for malignancy or other pathology. Postmenopausal bleeding is defined as vaginal bleeding that occurs after 12 months of amenorrhea, and it is a significant clinical concern due to the increased risk of endometrial cancer.

**Why the Correct Answer is Right**
The correct investigation of choice is a dilatation and curettage (D&C) with histopathological examination of the endometrial tissue. This procedure involves scraping the lining of the uterus to obtain a tissue sample for histopathological analysis. The endometrium is particularly susceptible to malignant transformation in postmenopausal women, and a D&C with histopathology is essential to rule out endometrial cancer or other pathology such as hyperplasia or atrophy.

**Why Each Wrong Option is Incorrect**
* **Option A:** Ultrasound is a useful tool for evaluating the endometrial thickness and identifying potential causes of bleeding, but it is not the investigation of choice for postmenopausal bleeding due to its inability to diagnose malignancy or other pathology.
* **Option B:** Endometrial biopsy is a less invasive alternative to D&C, but it may not be sufficient to rule out malignancy, especially in cases where the biopsy sample is small or inadequate.
* **Option C:** Hysteroscopy is a valuable tool for visualizing the uterine cavity and identifying potential causes of bleeding, but it is not the initial investigation of choice for postmenopausal bleeding due to its higher cost and invasiveness.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that postmenopausal bleeding is a "red flag" symptom that requires prompt investigation to rule out malignancy or other pathology. A high index of suspicion and thorough evaluation are crucial to ensure timely diagnosis and treatment.

**Correct Answer:** C. Hysteroscopy is a valuable tool for visualizing the uterine cavity and identifying potential causes of bleeding, but it is not the initial investigation of choice for postmenopausal bleeding due to its higher cost and invasiveness.