Consider the following binary search treeIn what order are the keys pushed onto the stack s when the mystery function is called with a pointer to the root of this tree?std::stack s $\{\}$;

void mystery$($Node$*$ current$)\{$

if $($current $==$ nullptr$)\{$

return;

$\}$

mystery$($current$->$leftChild$)$;

s$.$push$($current$->$data$)$;

mystery$($current$->$rightChild$)$;

s$.$pop$()$;

$\}$ The stack s here is a global variable which is empty when the mystery function is initially called.

For your referestruct Node $\{$

int data $\{\}$;

Node$*$ leftChild $\{\}$;

Node$*$ rightChild $\{\}$;

$\}$; Choose from the answers below:

a$.5,1,3,2,4,6,7$

b$.1,2,3,4,5,6,7$

c$.3,4,2,1,5,6,7$

d$.2,4,3,1,7,6,5$