请阅读短文
Several decades ago, the US sociologists went so far as to develop a series of universal facial images supposed to represent the seven basic human emotions: happiness, sadness, surprise, fear, disgust, anger and neutrality. But now, a new study by researchers at the University of Glasgow indicates that these standardized facial images aren't so universal after all.
For the study, the Scottish researchers found 13 Western Caucasians (mainly Europeans) and 13East Asians (mostly Chinese students). The volunteers were shown the standardized facial images and asked to identify the emotions being expressed. At the same time, the researchers electronically monitored the eye movements of the volunteers.
According to the results, published in the journal Current Biology, the Asian participants had a harder time than the Caucasians telling the difference between a face meant to look fearful compared with one showing surprise, and a face supposedly expressing disgust compared with one displaying anger. "This strongly suggests that the meanings of facial expressions are different across culture." says Rachael Jack, who led the study.
The study also showed that the volunteers focused on different parts of the face in their efforts to understand the underlying emotions. "Westerners look at both the eyes and the mouth to the same degree, yet Easterners favor the eyes and overlook the mouth. This means that Easterner shave difficulties distinguishing facial expressions that are similar around the eyes." Ms Jack says. The faces representing fear and surprise "both have big, wide open eyes, while the mouths are very different." She notes. "It would be difficult to distinguish between the two ... if you didn't look at the mouth."
So why would different cultures express emotions in different ways? Ms Jack thinks it may be considered impolite in some Asian cultures to display certain emotions in an obvious manner, and that they use more subtle ways to express them. In particular, muscle movements around their eyes could be more important for expressing feelings than over-expressive mouth movements, explaining why the Asian participants focused on the eyes, she says.

In the experiment, the East Asian volunteers had difficulties distinguishing between fear and surprise because__________.
查看材料

A．they found no differences between the mouths
B．they focused on the eyes and neglected the mouth
C．they were not good at reading facial expressions
D．Easterners express fear and surprise in the same way