binary search tree $($BST$)$ symbol table st$.$

a$.$ What is the height of the BST$,$ assuming the root to be at height $0?$

$($A$)5$

$($B$)6$

$7$

$($D$)4$

$($E$)8$

b$.$ What does at$.$rank$("0")$ return?

B

$($B$)7$

$($C$)5$

$($D$)9$

$($E$)6$