18) The enzyme poly-A polymerase is responsible for adding 3' poly-A tails to eukaryotic mRNAs. This enzyme... A. cuts the mRNA after recognition of the cleavage/polyadenylation signal by CstF and CPSF proteins. B. polymerizes the tail using an RNA template that is part of the enzyme. C. isthesameaspolII D. normally adds about 2000 A nucleotides to the mRNA. E. uses A TP as a substrate.