Exhausted and unhappy, you still have to squeeze a smile to your friends, or teachers. That's just life, you may think. But new research suggests that putting on a fake smile can worsen people's mood and even lower work efficiency. Lead researcher Brent Scott with other researchers studied a group of bus drivers for two weeks. They tried to find out what happened when the drivers were involved in "surface acting" or fake smiling, and the opposite, "deep acting" which means people put on real smiles by recalling pleasant memories or thinking about their current situation more positively. The results showed that on days when drivers were forced to smile, they felt depressed and didn't want to work. On days when they smiled due to positive thoughts, their mood improved a lot as well as their work efficiency. The research goes against the popular belief among companies that employees should be cheerful to customers at all times. They include employees of shops, banks, call center workers and others who have face-to-face contact with members of the public. "Smiling for the sake of  smiling can lead to emotional exhaustion and coldness, and that's bad for the organization," Scott told the Daily Mail. The study also showed that women were harmed more by fake smiling than men. Their mood and work performance both worsened more. But they were helped more by deep acting -- their mood became better and they worked more efficiently. However, while deep acting seemed to improve mood in the short term, Scott says it's not a long-term solution for unhappiness. "There have been some suggestions that if you do this over a long period that you start to feel inauthentic ," Scott said. "You may be trying to cultivate positive emotions, but at the end of the day you may not feel like yourself anymore." We can conclude from the article that the researchers think that   _  .
people should be true to their feelings smiling helps to put people in a good mood and become more efficient it is unnecessary to cultivate positive emotions deep acting can improve mood in the long run
Question: Exhausted and unhappy, you still have to squeeze a smile to your friends, or teachers. That's just life, you may think. But new research suggests that putting on a fake smile can worsen people's mood and even lower work efficiency. Lead researcher Brent Scott with other researchers studied a group of bus drivers for two weeks. They tried to find out what happened when the drivers were involved in "surface acting" or fake smiling, and the opposite, "deep acting" which means people put on real smiles by recalling pleasant memories or thinking about their current situation more positively. The results showed that on days when drivers were forced to smile, they felt depressed and didn't want to work. On days when they smiled due to positive thoughts, their mood improved a lot as well as their work efficiency. The research goes against the popular belief among companies that employees should be cheerful to customers at all times. They include employees of shops, banks, call center workers and others who have face-to-face contact with members of the public. "Smiling for the sake of  smiling can lead to emotional exhaustion and coldness, and that's bad for the organization," Scott told the Daily Mail. The study also showed that women were harmed more by fake smiling than men. Their mood and work performance both worsened more. But they were helped more by deep acting -- their mood became better and they worked more efficiently. However, while deep acting seemed to improve mood in the short term, Scott says it's not a long-term solution for unhappiness. "There have been some suggestions that if you do this over a long period that you start to feel inauthentic ," Scott said. "You may be trying to cultivate positive emotions, but at the end of the day you may not feel like yourself anymore." We can conclude from the article that the researchers think that   _  .
A. people should be true to their feelings
B. smiling helps to put people in a good mood and become more efficient
C. it is unnecessary to cultivate positive emotions
D. deep acting can improve mood in the long run
Answer: