4. Suppose that you are given a $100 budget at work that can be spent only on two items: staplers and pens. If staplers cost $10 each and pens cost $2.50 each, then the opportunity cost of purchasing one stapler is: LO1.4

a. 10 pens.

b. 5 pens.

c. zero pens.

d. 4 pens.