Answer:
B) losses you avoided by not buying a stock that has since decreased in price
Step-by-step explanation:
If a stock has not been bought, there has not been a transaction involving that particular stock. Even though, in theory, you may have avoided losses by not buying a stock that has decreased in price, there hasn't been any actual gain or loss on investment related to that stock since there was no investment.
Since all other alternatives present valid parameters when calculating return on investment, the answer is B).