问题：

[单选] How dose a DHCP server dynamically assign IP address to host?（）

A . Addresses are allocated after a negotiation between the server and the host to determine the length of the agreement.
B . Addresses are assigned for a fixed period of time.At the end of period,a newquest for an address must be made ,and another address is then assigned.
C . Addresses are leased to host.A host will usually keep the same address by periodically contacting the DHCP sever to renew the lease.
D . Addresses are permanently assigned so that the host uses the same address at all times.