**Core Concept**
The question tests knowledge of cervical cancer staging, specifically the involvement of the parametrium and pelvic structures. In cervical cancer staging, the involvement of the parametrium is a critical factor in determining the stage of the disease.

**Why the Correct Answer is Right**
The correct answer is related to the staging of cervical cancer when the parametrium is involved but not the pelvic wall or distant organs. Stage II cervical cancer is divided into two subcategories: Stage IIA and Stage IIB. Stage IIA involves the parametrium, whereas Stage IIB extends to the pelvic wall. Therefore, when the parametrium is involved but not the pelvic wall, the correct stage is Stage IIA.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Stage IIA involves the parametrium, but Stage II is the correct category when the parametrium is involved, not the specific subcategory Stage IIA.
**Option B:** This option is incorrect because Stage IIB involves the pelvic wall, which is not the case when the parametrium is involved but not the pelvic wall.
**Option C:** This option is incorrect because radiotherapy is not the primary treatment for Stage IIA cervical cancer; surgery is the preferred option.
**Option D:** This option is incorrect because hysterectomy is not the only treatment option for Stage IIA cervical cancer; other treatment options include radiation therapy and chemotherapy.

**Clinical Pearl / High-Yield Fact**
When staging cervical cancer, it's essential to differentiate between the involvement of the parametrium and the pelvic wall, as this affects the treatment plan and prognosis.

**Correct Answer: B. Stage II**