Karen Earned a Large Income by Buying Houses When They

Karen earned a large income by buying houses when they were selling for relatively low prices, and selling them at a later time when they were selling for relatively high prices. Which of the following theories of profit best describes the reason behind her success?

A) Uncertainty is the source of profits.
B) Profit is the reward for alertness to arbitrage opportunities.
C) Profit is the return to the entrepreneur as innovator.
D) Land is always a source of economic profit.
E) If you work hard enough, you will be rewarded.