The correct answer is: b. the removal of introns and alternative splicing of exons
Post-transcriptional regulation includes processes of regulation between transcription and translation such as RNA splicing, capping, addition of poly-A tail, RNA editing.
RNA splicing represents the process of RNA processing in which newly synthesized pre-mRNA transcript is converted into a mature mRNA. This process occurs only in eukaryotic organism and includes the removal of introns and joining together the exons. RNA splicing might occur during or immediately after transcription and it is performed by spliceosome (complex of small nuclear ribonucleo proteins).
Alternative splicing is a regulated process in which a single gene can code for multiple proteins because particular exons of a gene may be included within or excluded from the final mRNA.
There's a bunch of examples.
For example, hairlines. A widow's peak is a dominant trait over a straigh hairline.
Or dominant hand type. Right hands are dominated over left hands.
Or hair types. Curly hair dominates straight hair.
If you google it, you'll get a lot more examples.
Viruses are not made out of cells, they can't keep themselves in a stable state, they don't grow, and they can't make their own energy. Even though they definitely replicate and adapt to their environment, viruses are more like androids than real living organisms.