Which of the following is the prefix for address 1000:0000:0000:0001:0000:0000:0000:0000, assuming a mask of /64?

(A) 1000::1:10:0:0:0/64
(B) 1000:0:0:1::/64
(C) 2000:0:0:1::/64
(D) 1000::1::/64

1000:0:0:1::/64 is the correct answer. The /64 prefix length means that the last 64 bits, or last 16 digits, of the address, should be changed to all 0s. That process gives the unabbreviated prefix as 1000:0000:0000:0001:0000:0000:0000:0000. The last four quartets (last four sets of four hex digits) are all 0s, making that string of all 0s be the longest and best string of 0s to replace with ::. After removing the leading 0s in other quartets, the correct answer is: 1000:0:0:1::/64.