Virus which has more than one serotypes -

Ans. is 'd' i.e., Influenzao Influenza virus is an enveloped RNA virus containing 8 pieces (8 segments) of single stranded RNA.o There are three viral subtypes : (i) Type A (causes all pandemics and most epidemics); (ii) Type B: and (iii) Type C (not circulating currently).o Currently the influenza viruses circulating in the world are : H1 N1 of type A (causes swine flu); H2N2 of type A; H3 N2 of type A; H5N1 of type A (causes birdflu or avian influenza); H7 N9 of type A (caused epidemic of avian influenza in China in 2013); and type B.