Research for a Universal Flu Vaccine Tends to Focus on

Research for a universal flu vaccine tends to focus on

A) core proteins, as they do not mutate as rapidly as H and N spikes and they tend to be similar between different influenza strains.
B) H spikes as they mutate rapidly, allowing for more chances for the vaccine to work.
C) viral tails because they exist in all flu viruses and do not mutate often.
D) N spikes because they tend to be similar between different influenza strains.