16. Which of the following is true about protein targeting in eukaryotic cells? (A) Signal sequences are always located at the carboxyl terminus of a newly synthesized protein. (B) Polypeptides with signal sequences are moved into the Golgi apparatus as they are synthesized. (C) Proteins targeted to the nucleus have an internal signal sequence cleaved once the protein is successfully targeted. (D) Proteins targeted to mitochondria and chloroplasts do not use an amino-terminal signal sequence.