The Influenza Virus Gains Entry into a Host Cell by an Endocytotic

The influenza virus gains entry into a host cell by an endocytotic process.The viral nucleocapsid leaves the endosome and enters the cytoplasm through a membrane fusion mechanism.Fusion of the viral envelope with the endosomal membrane is facilitated by

A) a conformation change in the hemagglutinin to expose a fusion protein.
B) the production of a lipase by the influenza virus.
C) sialic acid residues of the receptor proteins.
D) specific viral protein recognition of pores in the endosome vesicle.
E) the production of proteases by the influenza virus.