Which of the following is the IPV$6$ loopback address?

$0000$:$0000$:$0000$:$0000$:$0000$:$0000$:$0000$:$1111$

FEDC::$00$CF:$1234$

::$1$

$127\mathrm{.}0\mathrm{.}0\mathrm{.}1$