**Core Concept**
Cervical cancer (Ca cervix) is a malignancy of the cervix uteri, with human papillomavirus (HPV) infection being the primary risk factor. The pathogenesis involves persistent high-risk HPV infection leading to cervical dysplasia and eventually invasive cancer.

**Why the Correct Answer is Right**
Option A is correct because approximately 90% of cervical cancer cases are associated with high-risk HPV types, such as HPV 16 and 18. HPV infection leads to the integration of viral DNA into the host genome, resulting in the expression of oncogenic proteins that disrupt normal cell cycle regulation. This ultimately leads to the development of cervical dysplasia and cancer. The high prevalence of HPV infection in cervical cancer cases underscores the importance of HPV vaccination and screening programs in preventing the disease.

**Why Each Wrong Option is Incorrect**
**Option B:** Nulliparity (never having given birth) is a risk factor for endometrial cancer, not cervical cancer. Cervical cancer is more commonly associated with factors such as HPV infection, early age at first intercourse, and multiple sexual partners.
**Option C:** Oral contraceptive pills (OCPs) are not a direct risk factor for cervical cancer. However, they may increase the risk of cervical dysplasia in women with underlying HPV infection. This is because OCPs may affect the immune system's ability to clear HPV infection.
**Option D:** Immunocompromised patients are at increased risk of various infections and malignancies, including cervical cancer. However, the primary risk factor for cervical cancer remains HPV infection, rather than immunocompromised status per se.

**Clinical Pearl / High-Yield Fact**
HPV vaccination is effective in preventing high-risk HPV types and subsequent cervical cancer. The vaccine is recommended for all females aged 11-26 years, and catch-up vaccination is recommended for females up to age 26 who have not been vaccinated previously.

**Correct Answer: A. 90% associated with HPV**