Q: Read the following article and answer the question. Article: Honesty is the best policy, as the English saying goes. Unfortunately, honesty often leaves us when no one is watching, British psychologists reported last week. Researchers at UK's Newcastle University set up an experiment in their psychology department's coffee room. They set a kettle, with tea, coffee and milk on the counter and hung up a sign listing the price for drinks. People helping themselves to a cup of tea were supposed to put a few cents in the box nearby. The scientists hung a poster above the money box, and changed each week between pictures of gazing eyes and pictures of flowers. The researchers found that staff paid 2.76 times more for their drinks when the image of the eyes was hung. "We were shocked by the size of the effect," said Gilbert Roberts, one of the researchers. Eyes are known to be a powerful perceptual signal for humans, scientists say. "Even though the eyes were not real, they still seemed to make people behave more honestly," said Melissa Bateson, a behavioral biologist and leader of the study. Researchers believe the effect throws light on our evolutionary past. It may arise from behavioral characteristics that developed when early humans formed social groups to strengthen their chances of survival. For social groups to work, individuals had to co-operate, rather than act selfishly. "There's an argument that if nobody is watching us, it is in our interests to behave selfishly. But when we're being watched we should behave better. So people see us as co-operative and behave the same way towards us," Bateson said. The new finding indicates that people have a striking response to eyes. That might be because eyes and faces send a strong biological signal we have evolved to respond to, Bateson said. The finding could be put to practical use. For example, images of eyes could ensure ticket sales on public transport and improve surveillance systems to deter anti-social behavior. Question: In the experiment, a poster was hung above the money box to _ . Answer:

Choices:
A). give a harmonious atmosphere.
B). remind people the drinks were not free.
C). prove the actual effect of different pictures.
D). see how honest people are in different situations.
The answer is:
D).