The First Step in the Post-Translational Processing of Secreted Proteins

The first step in the post-translational processing of secreted proteins in eukaryotes is:

A) Proteolytic removal of the first two or three amino acid residues from the amino terminus by the signal recognition particle.
B) Attachment of a mannose-rich oligopeptide to asparagine side chains.
C) Attachment of mannose-6-phosphate to the protein.
D) Proteolytic cleavage by signal peptidase.
E) Formation of disulfide bonds.