That a different component part of the vaccine is necessary is principally due to the variable change of ______.

A．Supervising the assessment of influenza virus strains.
B．Holding meetings twice a year to provide the latest data concerning the composition of the vaccines.
C．Publishing the related information in a WHO almanac.
D．Stressing the importance of preventing influenza for people living in tropical areas of Asi

A．most of them died of some sickness
B．their holidays and evenings have been ruined by their jobs
C．most of them are completely tired of the narrowly defined subject
D．most of their grants run out