a$)$ One can implement a stack based on a linked list so that all relevant push$/$pop operation is time O$(1).$

b$)$ One can not implement a stack $($of unbounded size$)$ based on an array so that each individual push$/$pop operation is time O$(1).$

c$)$ The core data structure of Depth$-$First Search is a stack.

d$)$ One can reverse the order of the elements in a singly linked list in time O$($N$).$

e$)$ It is possible to append two priority queues in time O$(1).$

f$)$ Adding an element to a Stack has worst$-$case time complexity O$($log$($N$)).$

g$)$ Returning the maximum element in a PriorityQueue $($larger the element, higher the priority$)$ can be done in time O$(1).$

g$)$ Returning the minimum element in a PriorityQueue $($larger the element, higher the priority$)$ can be done in time O$(1).$