[单选题]22.Butascasesofthevirusspreadandmultiply,callsforclosingbordershavegrownlouder,mostpredictablyfromthefarrightandpopulistswhowereneverfansofthebloc’sopenborderpolicy.whichofthefollowingcanbestreplace"multiply"in"casesofthevirusspreadandmultiply"?