What is the unique SPE of this game?

Note that the strategies are written as $($P$1\text{'}$s strategy,P$2\text{'}$s strategy,P$3\text{'}$s strategy$)$

$($C$,$B$,$A$)$

$($B$,$A$,$A$)$

$($A$,$A$,$A$)$

$($A$,$A$,$B$)$