What is IPv6 router solicitation?

A.
a request made by a node to join a specified multicast group
B.
a request made by a node for its IP address
C.
a request made by a node for the IP address of the DHCP server
D.
a request made by a node for the IP address of the local router
Explanation:
http://computernetworkingnotes.com/ipv6-features-concepts-and-configurations/ipv6-neighbor-discovery.html (See router solicitation)