**Core Concept**
Sterilization of culture media containing serum is a critical process to prevent contamination and ensure the reliability of microbiological and biochemical tests. The serum in culture media can be heat-sensitive and may not withstand high temperatures, making dry heat or radiation-based methods unsuitable for sterilization.

**Why the Correct Answer is Right**
The correct answer is gamma radiation, which is a widely used method for sterilizing heat-sensitive materials, including culture media containing serum. Gamma radiation inactivates microorganisms by damaging their DNA, preventing them from reproducing and causing infection. This process is particularly useful for sterilizing materials that cannot withstand high temperatures or moisture.

**Why Each Wrong Option is Incorrect**
**Option A:** Autoclaving is a method of sterilization that uses high-pressure steam to kill microorganisms. However, it is not suitable for sterilizing culture media containing serum, as the high temperatures and moisture can cause the serum to degrade.

**Option B:** Dry heat sterilization uses hot air to kill microorganisms and is not suitable for sterilizing culture media containing serum, as it can cause the serum to become denatured and lose its biological activity.

**Option C:** Filtration is a method of sterilization that uses a porous membrane to remove microorganisms from a liquid solution. However, it is not suitable for sterilizing culture media containing serum, as the serum can pass through the filter and still contain microorganisms.

**Clinical Pearl / High-Yield Fact**
Gamma radiation is a widely used method for sterilizing heat-sensitive materials, including culture media containing serum. This method is particularly useful for sterilizing materials that cannot withstand high temperatures or moisture, making it an essential technique in microbiological and biochemical testing.

**Correct Answer: D. Gamma radiation.**