RBTNode is a Java class for a node in a red$-$black tree. Which is the correct implementation of the

RBTNode class's areBothChildrenBlack$()$ method?

boolean areBothChildrenBlack$()\{$

if $($left$.$isRed$()||$ right.isRed$())\{$

return false;

$\}$

return true;

$\}$

boolean areBothChildrenBlack$()\{$

if $($left$.$isRed$()$ && right.isRed$())\{$

return false;

$\}$

return true;

$\}$

boolean areBothChildrenBlack$()\{$

if $($left $==$ null $||$ left.isRed$())\{$

return false;

$\}$

if $($right $==$ null $||$ right.isRed$())\{$

return false;

$\}$

return true;

$\}$

boolean areBothChildrenBlack$()\{$

if $($left $!=$ null && left.isRed$())\{$

return false;

$\}$

if $($right $!=$ null && right.isRed$())\{$

return false;

$\}$

return true;

$\}$