If you are unsure of which Internet Protocol version 6 address is valid, you can quickly go through the process of elimination. Answers B and C cannot be IPv6 addresses because of the inclusion of the letters G and H. Answer D is incorrect because it includes double colons.
This leaves answer A: 2031:0:130F::9C0:876A130B The reason that answer A is correct and has double colons is due to the fact that a line of zeroes have been suppressed—and done so correctly.
The answer for this is letter A. A has an ipv6 address that states 2031:0:130F:9C0:876A:130B. The other addresses are not valid because of different reasons. Right off the bat, we can see that D is not valid because of the double: . B is not valid because of the letter G. C is not a valid ipv6 address because this contains the letter H.
It will be wise to familiarize yourself with the different letters that should not be part of the usual ipv6 address. The more that you understand this, the easier it will be for you to eliminate some of the addresses that you have to choose from. Out of the various addresses, only A is valid.