IPv6 addresses are 128-bit hexadecimal addresses. Therefore, letters such as “G” and “H” contained in the second and third answers are invalid. The fourth answer contains two semi-columns “::”, which is also invalid, as the semi-column can only be used once in an IPv6 address.
More information on IPv6 can be found on Firewall. cx’s analysis of IPv6 Protocol structure and IPv6 subnetting.