What is the output of the following program? public class Stack { protected static final int CAPACITY = 100; protected int size,top = -1; protected Object stk[];   public Stack() { stk = new Object[CAPACITY]; }   public void push(Object item) { if(size_of_stack==size) { System.out.println("Stack overflow"); return; } else { top++; stk[top]=item; } } public Object pop() { if(top<0) { return -999; } else { Object ele=stk[top]; top--; size_of_stack--; return ele; } } }   public class StackDemo { public static void main(String args[]) { Stack myStack = new Stack(); myStack.push(10); Object element1 = myStack.pop(); Object element2 = myStack.pop(); System.out.println(element2); } }

• A. stack is full
• B. 20
• C. 0
• D. none of the mentioned