**Core Concept**
In eukaryotic cells, genes are transcribed into a precursor messenger RNA (pre-mRNA) that undergoes extensive processing before becoming the mature messenger RNA (mRNA). This process involves the removal of non-coding regions, known as introns, which are not essential for protein synthesis.

**Why the Correct Answer is Right**
The correct answer is a type of non-coding region that is removed during RNA splicing. The process of RNA splicing involves the recognition and removal of introns by the spliceosome, a complex of small nuclear ribonucleoproteins (snRNPs). The remaining exons are then joined together to form the mature mRNA, which is then translated into protein. The removal of introns is crucial for the efficient translation of eukaryotic genes, as introns can be toxic to the cell if left unspliced.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a type of coding region that is present in the mature mRNA. Exons are the coding regions of a gene that are retained in the mature mRNA and are essential for protein synthesis.
**Option B:** This option is incorrect because it refers to a type of RNA that is involved in the regulation of gene expression, but is not a type of non-coding region.
**Option C:** This option is incorrect because it refers to a type of RNA that is involved in the translation of mRNA into protein, but is not a type of non-coding region.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the removal of introns during RNA splicing can lead to the creation of alternative splice variants, which can result in different protein isoforms with distinct functions.

**Correct Answer:** C. Introns.