HowdoseaDHCPserverdynamicallyassignIPaddresstohost？（）

A.Addressesareallocatedafteranegotiationbetweentheserverandthehosttodeterminethelengthoftheagreement. B.Addressesareassignedforafixedperiodoftime.Attheendofperiod，anewquestforanaddressmustbemade，andanotheraddressisthenassigned. C.Addressesareleasedtohost.AhostwillusuallykeepthesameaddressbyperiodicallycontactingtheDHCPsevertorenewthelease. D.Addressesarepermanentlyassignedsothatthehostusesthesameaddressatalltimes.