In nature, what is the order of events in processing the product of the gene for insulin?

In nature, what is the order of events in processing the product of the gene for insulin?
 
  A) cleavage of 35 amino acids from the middle of the polypeptide to make two chains that are then joined by disulfide bonds
  B) cleavage of 24 amino acids from the N terminus to form proinsulin that is subsequently cleaved to make A and B chains
  C) removal of 5 leader sequence from the mRNA, and splicing out of a large central intron to produce the mRNA that codes for the final form of polypeptide
  D) removal of large mRNA sequences by RNA editing, followed by splicing of the products of the two insulin genes
  E) transcription of the two insulin genes A and B, translation, and posttranslational joining of the two polypeptides