**Core Concept**
UV radiation exposure leads to the formation of pyrimidine dimers, specifically cyclobutane pyrimidine dimers (CPDs), in DNA. This process is a critical step in the development of skin cancer and other sun-related diseases.

**Why the Correct Answer is Right**
UV radiation stimulates the formation of pyrimidine dimers through a process known as photoreaction. When UV radiation hits the skin, it causes adjacent pyrimidine bases (cytosine and thymine) to form a covalent bond, resulting in the formation of a cyclobutane ring. This process is mediated by the presence of UV-absorbing chromophores, such as DNA itself. The resulting pyrimidine dimers can lead to mutations and DNA damage, which can contribute to the development of skin cancer.

**Why Each Wrong Option is Incorrect**
**Option A:** Prevents formation of Pyrimidine dimers - This is incorrect because UV radiation actually stimulates the formation of pyrimidine dimers, not prevents it.
**Option C:** Purine dimers - This is incorrect because UV radiation primarily leads to the formation of pyrimidine dimers, not purine dimers.
**Option D:** None - This is incorrect because one of the options (B) is indeed correct, and UV radiation does stimulate the formation of pyrimidine dimers.

**Clinical Pearl / High-Yield Fact**
Remember the "ABCs" of UV radiation-induced DNA damage: Adenine and cytosine are not as susceptible to UV radiation-induced damage as thymine and cytosine, which form pyrimidine dimers. This is because adenine and guanine are not adjacent to each other in the DNA double helix, making them less prone to photoreaction.

✓ Correct Answer: B. Stimulates formation of Pyrimi dine dimmers