Which IPv6 address is valid?

Which IPv6 address is valid?
A . 2001:0db8:0000:130F:0000:0000:08GC:140B
B . 2001:0db8:0:130H::87C:140B
C . 2031::130F::9C0:876A:130B
D . 2031:0:130F::9C0:876A:130B

Answer: D

Explanation:

An IPv6 address is represented as eight groups of four hexadecimal digits, each group representing 16 bits (two octets). The groups are separated by colons (:). An example of an IPv6 address is 2001:0db8:85a3:0000:0000:8a2e:0370:7334.

The leading O’s in a group can be collapsed using ::, but this can only be done once in an IP address.