单项选择题

Many of us still tend to regard emotions as interfering with rational thought, and sometimes landing us in trouble. But in recent years psychologists have taken quite a different view. Keith Oatley, Professor of psychology at Glasgow University, is involved in the research which shows the fundamental importance of emotions. He believes we are very ambivalent about them: we think of our emotions as being irrational, but we also consider them as essential to being human.
For example, Mr. Spock, a character in the television series Startrek is super-intelligent, and he has no emotions at all! However, he is never made captain of the spaceship. Maybe, this is because Mr. Spock is not the kind of person you can identify with a person who shows his emotions. As Professor Oatley points out, our emotions have very important functions, for example, fear. If we cross the road and a car approaches, we usually freeze or step back. We stop what we were doing, check what we have done, and pay very careful attention to the environment. The emotion of fear calls into readiness this small repertoire ( 指令系统 ) of actions which, on average, helps preserve our safety.
On the other hand, if things are going well and small problems come up, we find we can solve them with the resources we have to hand. As a consequence, we tend to feel happy and usually continue doing the job. Anger is an emotion that tends to occur when someone is preventing us from doing something. Then this small "kit" of reactions enables us to prepare ourselves to be quite aggressive to that person, or to try harder, and so on. Professor Oatley believes emotions generally occur at these junctures in actions. With fear and anger oar emotions prompt us to start doing something else, whereas with happiness they "suggest" we continue what we are already doing.
By "we are very ambivalent about them" (Lines 3～4, Para. 1 ) it is meant that ______.