**Core Concept**
Nucleotides are fundamental building blocks of DNA and RNA, consisting of a nitrogenous base, a sugar molecule (deoxyribose in DNA and ribose in RNA), and a phosphate group. They play a crucial role in the transmission of genetic information.

**Why the Correct Answer is Right**
The correct answer is a nucleoside, which is a nucleotide lacking a phosphate group. Nucleosides are formed when a nitrogenous base is attached to a sugar molecule. This combination is essential for the synthesis of nucleic acids, such as DNA and RNA. The removal of a phosphate group from a nucleotide results in a nucleoside, highlighting the critical role of phosphate groups in nucleotide structure and function.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incomplete and does not accurately describe a type of nucleotide or nucleoside.
* **Option B:** This option might describe a type of nucleotide, but it's not the correct answer, and the explanation is needed to understand why it's incorrect.
* **Option C:** This option could be referring to a different biomolecule, but it's not the correct answer in this context.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that nucleosides are the building blocks of nucleotides, which are in turn the fundamental components of DNA and RNA. This understanding is crucial for grasping the mechanisms of nucleic acid synthesis, repair, and replication.

**Correct Answer: C. Nucleoside. A nucleoside is a nucleotide lacking a phosphate group.**