The signal sequences are typically _______ residues long, rich in _____ charged residues such as arginines as well as hydroxyl residues such as serines and threonines, but devoid of ______ charged residues.

• A. 28 to 80, positively, negatively
• B. 300 to 800, negatively, positively
• C. 28 to 80, negatively, positively
• D. 300 to 500, positively, negatively