Wilbur​ Rickhiser, a financial​ advisor, recently told one of his​ clients: "The biggest mistake you can make is to hold onto a stock for too long in order to avoid a loss.​ Let's say you bought a stock for​ $50 per share but that six months later the price fell to​ $40 after a poor earnings report. Many of my clients in this situation will hold the​ stock, hoping the price will later rise above​ $50. In most cases like this the price does not rise and may even fall. You must know when to cut your​ losses." Which of the following is the best explanation for​ Rickhiser's advice? A. People often fail to ignore the sunk costs of their decisions. The cost of the stock bought at​ $50 per share is a sunk cost. B. People sometimes make mistakes when they buy stocks or when they buy goods and​ services: they ignore the monetary opportunity costs of their choices. C. People sometimes buy stocks because other people are buying them or they want to appear to be fashionable. D. People sometimes make mistakes when they buy stocks because of the endowment effect.