"Not so," say scientists John Barley and Bib Fatane. These men went beyond the headlines to probe the reasons why people didn't act. They found that a person has to go through two steps before he can help. First he has to notice that is an emergency.
Suppose you see a middle-aged man fall to the side-walk, is he having a heart attack？ Is he in a coma from diabetes？ Or is he about to sleep off a drunk？
Is the smoke coming into the room from a leak in the air conditioning？ Is it "steam pipes", Or is it really smoke from a fire？ It's not always easy to tell if you are faced with a real emergency.
Second, and more important, the person faced with an emergency must feel personally responsible. He must feel that he must help, or the person won't get the help he needs.
The researchers found that a lot depends on how many people are around. They had college students in to be "tested." Some came alone. Some came with one or two others. And some came in large groups. The receptionist started them off on the "tests." Then she went into the next room. A curtain divided the "testing room" and the room into which she went.
Soon the students heard a scream, the noise of file cabinets falling and cry for help. All of this had been pre-recorded on a tape-recorder.
Eight out of ten of the students taking the test alone acted to help. Of the students in pairs, only two out of the ten helped. Of the students in group, none helped.
In other words, in a group, Americans often fail to act. They feel that others will act. They, themselves, needn't. They do not feel any direct responsibility.
Are people bothered by situation where people are in trouble？ Yes, scientists found that the people were emotional, they sweated, they had trembling hands. They felt that other person's trouble. But they did not act. They were in a group. Their actions were shaped by the actions of those they were with.
The purpose of the passage is ______.

A. to explain why people fail to act in emergencies
B. to explain when people will act in emergencies
C. to explain what people will do in emergencies
D. to explain how people feel in emergencies