Answer:
The answer is (b.)The sending IPv6 router creates an IPv6 datagram and puts it in the data field of an IPv4 datagram.
Step-by-step explanation:
Since both routers are ipv6 versions and are connected together by intervening ipv4 router, then using tunneling method of connection, the best way would be for the sending ipv6 router to create an ipv6 datagram and then put it in the data field of an ipv4 datagram.