In a post-transcriptional modification called tailing, ___A_____ residues are added at the ___B_____ of mRNA.

	A	B
1.	adenylate	5' end
2.	guanylate	3' end
3.	adenylate	3' end
4.	guanylate	5' end

• A

  1

• B

  2

• C

  3

• D

  4