From the given expression tree, identify the infix expression, evaluate it and choose the correct result.

What is the time complexity of push operation in a stack implemented using an array?

A. O(1)

B. O(n)

C. O(log n)

D. O(n log n)

Which of the following operations is performed last in a stack?

A. Push

B. Pop

C. Peek

D. Size

What is the stack's behavior when it's described as LIFO?

A. Last In First Out

B. Last In Last Out

C. First In First Out

D. First In Last Out

How can you implement a stack using a linked list?

A. By using a singly linked list

B. By using a doubly linked list

C. By using a circular linked list

D. All of the above