**Core Concept**
Purine and pyrimidine synthesis are critical processes in nucleotide metabolism. These molecules serve as the building blocks for DNA and RNA, and their dysregulation can lead to various diseases. In this context, identifying common substrates for purine and pyrimidine synthesis is essential for understanding these metabolic pathways.

**Why the Correct Answer is Right**
The common substrates for purine and pyrimidine synthesis are ribose-5-phosphate and phosphoribosyl pyrophosphate (PRPP). Ribose-5-phosphate is a key intermediate in the pentose phosphate pathway and serves as the precursor for the synthesis of purine and pyrimidine nucleotides. Phosphoribosyl pyrophosphate (PRPP) is a high-energy molecule that donates a ribose group to the synthesis of purine and pyrimidine nucleotides. The enzyme PRPP synthetase catalyzes the formation of PRPP from ribose-5-phosphate and ATP.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided.
* **Option B:** This option is not provided.
* **Option C:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the synthesis of purine and pyrimidine nucleotides is tightly regulated to prevent overproduction, which can lead to the accumulation of toxic compounds and contribute to disease states such as gout and cancer.

**Correct Answer:** A.