What is the role of neighbor solicitation (NS) messages in the autoconfiguration of an IPv6 address?

A.
An IPv6 node sends an NS message to inform a node undergoing autoconfiguration that it is
already using a particular address.

B.
An IPv6 node sends an NS message for its tentative address to determine whether another
node is using it.

C.
An IPv6 node sends an NS message for the global prefix to prompt other IPv6 nodes to
advertise the addresses that they are using on that prefix.

D.
An IPv6 node sends an NS message to prompt an IPv6 router on the link to advertise the global
prefixes associated with the link immediately.

Explanation:
Duplicate Address Detection
When a host first joins a link, it multicasts neighbor solicitations for its own IPv6 address for a short
period before attempting to use that address to communicate. If it receives a neighbor
advertisement in response, the host realizes that another neighbor on the link is already using that
address. The host will mark the address as a duplicate and will not use it on the link.
Note that this process is similar to IPv4 gratuitous ARP requests, but NDP elegantly allows for
detection of two hosts with the same address before both hosts are actively sending traffic from
the address.
Note: Address Resolution
The function of address resolution was handled by ARP for IPv4, but is handled by ICMPv6 for
IPv6. In a process very similar to router discovery, two ICMPv6 messages are used: Neighbor
Solicitation (type 135) and Neighbor Advertisement (type 136). A host seeking the link layer
address of a neighbor multicasts a neighbor solicitation and the neighbor (if online) responds with
its link layer address in a neighbor advertisement.