Which three addresses are valid forms of an IPv6 Address: 2001:0DB8:0000:FE01:0000:0000:0000:0000? (Choose three.)

2001:0DB8:0000:FE01:: is valid because the four trailing all-zero groups (0000:0000:0000:0000) are legitimately collapsed into a single '::' - leading zeros within retained groups may optionally remain.

2001:DB8:0:FE01:: is valid because leading zeros are stripped from each group (0DB8 becomes DB8, 0000 becomes 0) and the four trailing zero groups are collapsed into '::', following both compression rules simultaneously.

2001:0DB8::FE01:: is invalid because it uses '::' twice - IPv6 rules permit only one '::' substitution per address to prevent ambiguity when expanding the omitted groups.

2001:DB8:0:FE01:0:0:0:0 is valid because it retains all eight groups with only leading zeros stripped, which is a correct full-length expanded representation without any '::' compression.