**Core Concept**
Secondary level of prevention aims to detect and treat problems early before they become more severe, thereby preventing complications and reducing the risk of progression. This level of prevention focuses on the early detection of disease through screening, which enables timely intervention to prevent or minimize the impact of the disease.

**Why the Correct Answer is Right**
Cervical Pap smear checking is an example of secondary level of prevention because it involves the early detection of cervical cancer or its precursors through a screening test. This allows for the treatment of abnormal cells before they become cancerous, thereby preventing the development of invasive cancer. The Pap smear is a widely used screening test that has been shown to be effective in reducing the incidence and mortality of cervical cancer.

**Why Each Wrong Option is Incorrect**
**Option A:** Prophylactic drug administration is a form of primary prevention, which aims to prevent the occurrence of disease before it occurs. This can be achieved through the use of medications to prevent the disease from developing in the first place.
**Option B:** Admitting a disabled child to a special school is an example of tertiary level of prevention, which focuses on the rehabilitation and management of established disease to prevent further complications and improve the quality of life. This level of prevention is more focused on managing the consequences of disease rather than preventing it.
**Option C:** Vaccination is also a form of primary prevention, which aims to prevent the occurrence of disease through the administration of a vaccine. Vaccines work by stimulating the body's immune system to produce antibodies that can recognize and attack specific pathogens, thereby preventing the disease from occurring.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the levels of prevention are not mutually exclusive, and different interventions can overlap across levels. However, understanding the primary, secondary, and tertiary levels of prevention can help healthcare professionals and policymakers design effective strategies to prevent and manage diseases.

**Correct Answer:**
✓ Correct Answer: D. Cervical pap smear checking