In the process of eukaryotic pre-mRNA splicing, how is the lariat intermediate formed?
a. By joining the 3' end of the intron to the 2' carbon of the branch site b. By joining the 5' end of exon 2 to the 2' carbon of the branch site
c. By joining the 5' end of the intron to the 2' carbon of the branch site d. By joining the 3' end of exon 1 to the 2'carbon of the branch site