Which of the following is the first event in the post-translational processing of an E.coli tRNA?

A)ribonuclease P cleavage to create the proper 5' end of the molecule
B)methylation of guanine residues
C)conversion of some uridine residues to pseudouridine
D)endonuclease cleavage of about 170 bases from the 3' end of the molecule
E)removal of 9 nucleotides from the 3' end by ribonuclease D