**Core Concept**
Post-exposure immunization refers to the administration of vaccines or immunoglobulins to prevent the development of a disease after exposure to a pathogen. This concept is crucial in public health and preventive medicine to mitigate the spread of infectious diseases.

**Why the Correct Answer is Right**
The correct answer involves two options: Rabies (a) and Measles (c). **Post-exposure prophylaxis (PEP) for rabies** typically involves immediate wound cleaning and administration of rabies immunoglobulin (RIG) along with a series of rabies vaccinations. This combination of RIG and vaccine is critical in preventing the development of rabies after exposure to the virus. **Post-exposure vaccination for measles**, on the other hand, is not a standard practice, as the measles vaccine is usually administered in a two-dose schedule as part of routine childhood immunization. However, in some cases, a single dose of measles vaccine may be recommended as post-exposure prophylaxis for individuals who are not immune to measles and have been exposed to the virus.

**Why Each Wrong Option is Incorrect**
**Option A:** Rabies (a) is correct, so no explanation needed.
**Option B:** Pertussis (b) is not typically given as post-exposure immunization; instead, antibiotics are used to treat exposed individuals.
**Option C:** Measles (c) is correct, so no explanation needed.
**Option D:** Yellow fever (d) vaccine is usually administered before traveling to endemic areas, not as post-exposure immunization.

**Clinical Pearl / High-Yield Fact**
In cases of post-exposure rabies, the administration of rabies immunoglobulin (RIG) is crucial, as it provides immediate protection against the virus until the vaccine takes effect.

**✓ Correct Answer: B. ac. Rabies and Measles.**