**Core Concept**
Ribose is a five-carbon sugar, specifically a pentose, that serves as a building block for nucleic acids such as RNA and DNA. The structure of ribose molecules is critical for their function in cellular processes.

**Why the Correct Answer is Right**
The correct answer is related to the chemical structure of ribose, which contains five carbon atoms (C5H10O5) and a specific number of hydroxyl (-OH) groups. Each carbon atom in the sugar ring is bonded to a hydroxyl group, except for the carbon atom that is part of the aldehyde group at one end of the molecule. This results in a total of four hydroxyl groups in the ribose molecule. The correct number of -OH groups in ribose is essential for its interaction with other molecules, such as nucleobases, during the synthesis of nucleic acids.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately reflect the number of hydroxyl groups in a ribose molecule.
* **Option C:** This option is incorrect because it suggests a higher number of hydroxyl groups than actually present in ribose.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the structure of ribose molecules is critical for their function in nucleic acid synthesis, and small changes to their structure can have significant effects on cellular processes.

**Correct Answer:** B. 4