题目内容：
阅读材料，回答题。Not all memories are sweet. Some people spend all their lives trying to forget bad experiences. Violence and traffic accidents can leave people with terrible physical and emotional scars. Often they relive these experiences in nightmares( 噩梦).
Now American researchers think they are close to developing a pill, which will help people forget bad memories. The pill is designed to be taken immediately after a frightening experience. They hope it might reduce, or possibly erase ( 抹去), the effect of painful memories.
In November, experts tested a drug on people in the US and France. The drug stops the body releasing chemicals that fix memories in the brain. So far the research has suggested that only the emotional effects of memories may be reduced, not that the memories are erased.
The research has caused a great deal of argument. Some think it is a bad idea, while others support it.
Supporters say it could lead to pills that prevent or treat soldiers’ troubling memories after war. They say that there are many people who suffer from terrible memories.
"Some memories can ruin people’s lives. They come back to you when you don’t want to have them in a daydream or nightmare. They usually come with very painful emotions. " said Roger Pitman, a professor of psychiatry at Harvard Medical School. "This could relieve a lot of that suffering. "
But those who are against the research say that it is very dangerous to change memories because memories give us our identity(物质） They also help us all avoid the mistakes of the past."All of us can think of bad events in our lives that were horrible at the time but make us who we are. I’m not sure we want to wipe those memories out," said Rebecca Dresser, a medical ethicist.
The passage is mainly about ______ A．a new medical invention
B．a new research on memories
C．a way of erasing painful memories
D．an argument about the research on the pill
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