What is the function of the spliceosome?A-The spliceosome transcribes mitochondrial and chloroplast genes.B-The spliceosome removes the introns and joins the exons to form the mature transcript.C-The spliceosome removes the Shine-Delgarno sequence from the 5' end of the mRNA.D-The spliceosome adds a stretch of about 170 adenine nucleotides to the 3' end of the mRNA.E-The spliceosome adds a 7-methylguanosine residue to the 5' end of the mRNA.