**Core Concept**
A complete molar pregnancy is a type of gestational trophoblastic disease (GTD) characterized by the abnormal growth of trophoblastic cells, resulting in the formation of a non-viable embryo with no fetal parts. The risk of subsequent gestational trophoblastic neoplasia (GTN) is a significant concern in these patients.

**Why the Correct Answer is Right**
The risk of subsequent GTN in complete molar pregnancy is high, and it is estimated to be around 20-30%. This is because the abnormal trophoblastic cells can persist and potentially invade the myometrium, leading to persistent GTD (hydatidiform mole) or gestational trophoblastic neoplasia (GTN). The most common form of GTN is invasive mole or choriocarcinoma. The risk of GTN is higher in patients with complete molar pregnancies compared to partial molar pregnancies.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the risk of subsequent GTN in complete molar pregnancy is not around 5-10%. The actual risk is higher, as mentioned earlier.
* **Option B:** This option is incorrect because the risk of subsequent GTN in complete molar pregnancy is not related to the age of the patient. While age can be a factor in the development of GTD, it is not directly related to the risk of subsequent GTN in complete molar pregnancy.
* **Option C:** This option is incorrect because the risk of subsequent GTN in complete molar pregnancy is not directly related to the presence of a beta-hCG level greater than 100,000 mIU/mL. While high beta-hCG levels can be associated with GTD, a level of 100,000 mIU/mL is not a specific threshold for predicting the risk of subsequent GTN.

**Clinical Pearl / High-Yield Fact**
It is essential to monitor patients with complete molar pregnancies for signs of GTN, including vaginal bleeding, pelvic pain, and elevated beta-hCG levels. Regular follow-up and serial beta-hCG measurements are crucial in detecting early signs of GTN.

**Correct Answer:** D. 30%.