## Core Concept
RNA processing is a critical step in the synthesis of mature RNA molecules from precursor RNA transcripts. This process involves several modifications to the RNA transcript, including splicing, capping, and polyadenylation, which are essential for generating functional RNA molecules.

## Why the Correct Answer is Right
The correct answer, **C. Histone modification**, is related to chromatin modification rather than RNA processing. RNA processing primarily involves:
- **Splicing (A)**: removal of introns and joining of exons to form a continuous coding sequence.
- **5' capping (B)**: addition of a methylated guanine nucleotide to the 5' end of the RNA transcript, which protects the RNA from degradation and aids in its export from the nucleus.
- **Polyadenylation (D)**: addition of a poly(A) tail to the 3' end of the RNA transcript, which also protects the RNA from degradation and enhances its translation.

## Why Each Wrong Option is Incorrect
- **Option A: Splicing** is a crucial step in RNA processing, as it removes non-coding regions (introns) and joins coding regions (exons) together.
- **Option B: 5' capping** is essential for the stability and nuclear export of the RNA transcript.
- **Option D: Polyadenylation** adds stability to the RNA and facilitates its translation into protein.

## Clinical Pearl / High-Yield Fact
A key point to remember is that defects in RNA processing can lead to various diseases, including cancer and genetic disorders. For example, mutations affecting splicing factors can lead to diseases like myelodysplastic syndrome.

## Correct Answer: C. Histone modification