单选题 Honesty is the best policy, as the English saying goes. Unfortunately, honesty often deserts us when nobody 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 or coffee were supposed to put a few cents into a box nearby.
The scientists hung a poster above the money box and alternated each week between images 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.
"Frankly 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 the leader of the study.
Researchers believe the effect throws light on our evolutionary past. It may arise from behavioral traits that developed when early humans formed social groups to strengthen their chances of survival. For social groups to work, individuals had to cooperate, 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 are being watched we should behave better. So people see us as co-operative and behave the same way towards us," one scientist said.
The new finding indicates that people have striking response to eyes. That might be because eyes and faces send a strong biological signal we have evolved to respond to.
The finding can be put to practical use. For example, images of eyes could boost ticket sales on public transport and improve surveillance systems to prevent antisocial behavior.
The main idea of the passage is that

• A. humans have a stronger response to eyes than to flowers.
• B. photos of human eyes have a positive effect on people's behavior.
• C. the scientists' new finding may have many practical uses.
• D. people may behave dishonestly when there's no one aroun