Match the purpose with its DHCP message type. (Not all options are used.)

The DHCPDISCOVER message is used to identify any DHCP servers on a network. The DHCPOFFER message is used by a server to offer a lease to a client. The DHCPREQUEST message is used to identify both the specific DHCP server and the lease that the client is accepting.
The DHCPACK message is used by a server to finalize a successful lease with a client.
The DHCPNAK message is used when an offered lease is no longer valid.