在分析证券组合的可行域时，其组合线实际上在期望收益率和标准差的坐标系中描述了证券A和
题型：单项选择题
问题：
在分析证券组合的可行域时，其组合线实际上在期望收益率和标准差的坐标系中描述了证券A和证券B（）组合。
A．收益最大的
B．风险最小的
C．收益和风险均衡的
D．所有可能的
题型：单项选择题
阅读理解。
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 experiences in nightmares.
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 wipe out 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 wiped out. They are not sure
to what degree people's memories are affected.
The research has causeda 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 maybe the pills can change people's memories and
changing memories is very dangerous because memories give us our identity. They also help us all avoid
the mistakes of the past.
"All of us can think of bad events in our lives that were terrible 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.
1.The passage is mainly about .
A. a new medical invention
B. a new research on the pill
C. a way of wiping out painful memories
D. an argument about the research on the pill
2.We can infer from the passage that .
A. experts are not sure about the effects of the pills.
B. the pill will certainly stop people's emotional memories
C. taking the pill will do harm to people's physical health
D. the pill has already been produced and used by the public in America
3.Which of the following does Rebecca Dresser agree with in the last paragraph?
A. some memories can ruin people's lives.
B. people want to get rid of bad memories.
C. experiencing bad events makes us different from others.
D. the pill will reduce people's sufferings from bad memories.
4. You may probably read the passage in
A. a guidebook
B. a textbook
C.a medical magazine
D. a science fiction