1. Which of the following is not a valid postfix expression?

5 4 +

6 5 4 + -

4 + 5

8 2 + 2 /

all of the above are valid postfix expressions

2.

What is the result of evaluating the following postfix expression: 4 8 + 2 *

		40
		24
		64
		20
		none of the above are correct

3.

What exception is thrown if the pop method is called on an empty stack?

		EmptyStackException
		NoSuchElementException
		ArrayOutOfBoundsException
		EmptyCollectionException
		none of the above

4.

Which of the following methods removes an element from a queue?

		enqueue
		dequeue
		first
		pop
		push

5.

Which of the following methods inserts an element into a stack data structure?

		enqueue
		dequeue
		push
		pop
		peek

6.

A queue is helpful in implementing a __________________ sort.

		insertion
		selection
		quick
		radix
		merge