Which of the following contribute to new epidemics and the long-term survival of the influenza virus ...

Which of the following contribute to new epidemics and the long-term survival of the influenza virus in the human population? (Select all that apply.)
 
  a. New viral strains possess epitopes not recognized by antibodies made in the previous epidemic.
  b. The first influenza strain provoking a primary immune response constrains the types of antibodies made during a subsequent encounter with a different strain.
  c. The virus loses the capacity to express hemagglutinin, thereby rendering neutralizing antibodies useless.
  d. The virus uses gene rearrangement to achieve antigenic variation, which creates new epitopes.
  e. The RNA genome of the influenza virus is subject to point mutations during viral replication.