**Core Concept**
Carcinoma endometrium, also known as endometrial cancer, is a malignancy of the uterine lining. Predisposing factors play a crucial role in the development of this cancer. The underlying concept being tested here involves identifying risk factors that contribute to the development of endometrial cancer.

**Why the Correct Answer is Right**
Endometrial cancer is primarily influenced by hormonal, genetic, and lifestyle factors. Obesity is a significant risk factor due to its association with insulin resistance, which leads to increased levels of insulin and insulin-like growth factor-1 (IGF-1). These hormones promote cell proliferation and survival in the endometrium, increasing the risk of cancer. Additionally, genetic mutations, such as PTEN and KRAS, can also predispose individuals to endometrial cancer.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because nulliparity (never having given birth) is actually a risk factor for endometrial cancer, not a protective factor. Nulliparous women have a higher risk of developing endometrial cancer due to prolonged exposure to estrogen without the protective effects of pregnancy.
* **Option B:** This option is incorrect because unopposed estrogen exposure is a known risk factor for endometrial cancer. This can occur due to estrogen-only hormone replacement therapy or anovulatory menstrual cycles, which lead to unopposed estrogen stimulation of the endometrium.
* **Option C:** This option is incorrect because hypertension is not a direct risk factor for endometrial cancer. However, it is worth noting that some studies have suggested a possible link between hypertension and endometrial cancer risk, but this is still a topic of debate.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that obesity is a modifiable risk factor for endometrial cancer. Lifestyle modifications, such as weight loss and increased physical activity, can help reduce the risk of developing this cancer.

**Correct Answer: A. Nulliparity. Nulliparity is a known risk factor for endometrial cancer.**