Which of the following contains the three posttranscriptional modifications often seen in the maturation of mRNA in eukaryotes?

A) 5' -capping, 3' -poly(A) tail addition, splicing
B) removal of exons, insertion of introns, capping
C) heteroduplex formation, base modification, capping
D) 3' -capping, 5' -poly(A) tail addition, splicing
E) 5' -poly(A) tail addition, insertion of introns, capping