Expand hrRNA.

Explanation

**Step-by-Step Solution:**

1. **Identify the abbreviation**: The question asks to expand "hrRNA". The first step is to recognize that "hrRNA" is an abbreviation.

2. **Expand the abbreviation**: "hrRNA" stands for "heterogeneous nuclear RNA". This is the full form of the abbreviation.

3. **Understand the significance**: Heterogeneous nuclear RNA (hrRNA) is a type of RNA that is found in the nucleus of eukaryotic cells. It is important to note that hrRNA is a precursor to messenger RNA (mRNA).

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