Answer:
B (Enzymes cut introns out of an mRNA strand)
Step-by-step explanation:
When an RNA transcript is first made in an eukaryotic cell, it is considered a pre-mRNA. Eukaryotes undergo processing of the pre-mRNA strand immediately after transcription. The genes of an eukaryote are split up into parts that are expressed as RNA products and parts that are not. The parts that contains the actual coding regions and are expressed are called EXONS while the parts removed from in between the exons and referred to as "junk sequences" are called INTRONS.
Introns and exons alternate with each other along the length of the gene. Introns are usually considered the non-coding regions because they don't seem to code for any protein, hence they are removed before the mRNA product is finally ready for translation. This post- transcriptional process is called RNA SPLICING. RNA SPLICING can be likened to the process of removing the chaff (introns) from the wheat (exons). It is the removal of introns and joining of exons in eukaryotic mRNA.
Splicing is carried out by SPLICEOSOMES ( a protein and RNA complex), which removes introns from the genes in mRNA. They locate the ends of the INTRONS, cut them away from the EXONS, and join the ends of adjacent exons together. Once the entire gene is devoid of introns, the process of RNA splicing is complete.
It is worthy to note that, not only do the introns not carry information to build a protein, they actually have to be removed in order for the mRNA to encode a protein with the right sequence. If the spliceosome fails to remove an intron, an mRNA with extra "junk" in it will be made, and a wrong protein will get produced during translation.