Final answer:
Alternative RNA splicing results in different proteins from a single mRNA by varying exon and intron combinations, acting as a form of gene regulation and increasing protein diversity, but does not increase transcription rate. The correct answer is 'd. B and C only'.
Step-by-step explanation:
Alternative RNA splicing is the post-transcriptional process by which different protein products can be produced from a single gene. This is achieved by varying the combinations of exons and introns that are removed from the primary transcript. The process is regulated by the cell, which controls the frequency of different splicing alternatives as a form of gene regulation. As a result, alternative splicing allows for a diversity in protein products from the same gene, which can have vastly different sizes and amino acid sequences, thereby increasing the functional capacity of a single gene. It is important to note, however, that alternative splicing does not increase the rate of transcription but rather increases the variety of mRNA, and consequently, the proteins produced. In response to the question, the correct answer is 'd. B and C only' because alternative RNA splicing can allow the production of proteins of dramatically different sizes and amino acid sequences from a single mRNA, but it does not directly increase the rate of transcription.