Emotion is a feeling about or reaction to

题目：

Emotion is a feeling about or reaction to certain important events or thoughts. People enjoy feeling such pleasant emotions as love, happiness, and contentment. They often try to avoid feeling unpleasant emotions, such as loneliness, worry, and grief.
Individuals communicate most of their emotions by means of words, a variety of sounds, facial expressions, and gestures. For example, anger causes many people to frown, make a fist, and yell. People learn ways of showing some of their emotions from members of their society, though heredity (遗传)may determine some emotional behavior. Research has shown that different isolated peoples show emotions by means of similar facial expressions.
Charles Darwin, famous for the theory of natural selection, also studied emotion. Darwin said in 1872 that emotional behavior originally served both as an aid to survival and as a method of communicating intentions. According to the James-Lange theory of emotions developed in the 1880s, people feel emotions only if aware of their own internal physical reactions to events, such as increased heart rate or blood pressure. But this theory was not up-held: by research on cats that had their nervous system damaged. The cats could not feel their body’s internal changes, but they showed normal emotional behavior. John B. Watson, an American psychologist who helped found the school of psychology called behaviorism, observed that babies stimulated by certain events showed three basic emotions--fear, anger, and love. Watson’s view has been challenged frequently since he proposed it in 1919.
The most widely accepted view is that emotions occur as a complex sequence of events. The sequence begins when a person encounters an important event or thought. The person’s interpretation of the encounter determines the feeling that is likely to follow. For example, someone who encounters a bear in the woods would probably interpret the event as dangerous. The sense of danger would cause the individual to feel fear. Each feeling is followed by physical changes and desires to take action, which are responses to the event that started the sequence. Thus, a person who met a bear would probably run away.
Several American psychologists independently developed the theory that there are eight basic emotions. These emotions--which can exist at various levels of intensity--are anger, fear, joy, sadness, acceptance, disgust,
surprise, and interest or curiosity. They combine to form all other emotions, just as certain basic colors produce all others.

The main purpose of this writing is to ______.

A. arouse readers’ interest in emotional behaviors
B. help readers enjoy pleasant emotions
C. outline the development of theories about emotions
D. analyze various emotions and physical changes