The stock returns on Friday tend to be higher than on Monday. Researchers explain it with the fact that on Monday investors tend to be in a bad mood (because of the start of the working week) and therefore interpret all news in a negative way. On the contrary, on Friday investors tend to be in a good mood (because of the approaching weekend) and therefore interpret all news in a positive way. If there are no limits to arbitrage, then rational investors will be able to exploit these return patterns by: a. Buying stocks at the end of the trading day on Monday and selling them at the end of the trading day on Friday b. Short selling stocks at the end of the trading day on Monday and buying them at the end of the trading day on Friday c. Buying stocks at the end of the trading day on Friday and selling them at the end of the trading day on Monday (the following week)