We've been looking at fear from biological perspective. And someone asked whether the tendency to be fearful is genetic. While some study done with mice indicate that mammals do inherit fearfulness to some degree. In one study for instance, a group of mice were placed in the bright lit open boxes with no hiding places. Some of the mice wondered around the box and didn't appear to be bothered about being so exposed. But other mice didn't move. They stayed up against one wall, which indicate that they were afraid. Well, when fearful mice or you might say anxious mice like ones who stayed in one place. When mice like this were bred with one another repeatedly, after about 12 or so generations, then all of the offspring show similar signs of fearfulness. And even when the new born mouse from this generation was raised by a mother and with other mice who were not fearful, that mice still tend to be fearful as the result. Now, why is this? Well, it's thought that the specific gene in animal body have influenced on the anxious behavior. These genes that are associated with particular nerve cell receptors in brain. And the degree of overall fearfulness in the mammal seem to depend in the large part on the presence or absence of these nerve cell receptors. And this appears to apply to humans as well by the way. But while the tendency towards anxiety and fear may well be an inherited trait, but the specific form that the fear takes has more to do individual environment. So a particular fear like the fear of snakes or the fear of spider, say, is not genetic. But the overall tendency to have fearful responses is.
解析
How did some of the mice in the study demonstrated that they were afraid?
细节题。根据But other mice didn’t move．They stayed up against one wall，which indicate that they were afraid．可知研究中的老鼠靠在墙边，说明它们很害怕。因此，正确答案为D。