How is the poly(A)tail added to the 3' ends of the mRNAs produced during infection with a influenza virus?

A) The viral polymerase stutters at a poly(U) sequence.
B) The cellular poly(A) polymerase adds it.
C) Influenza virus mRNAs do not have poly(A) tails.
D) The viral poly(A) polymerase adds it after the mRNA is released from the template.
E) The entire poly(A) tail is encoded in the genome.