题目内容：

More than loo genes are related with increased risk of developing schizophrenia（精神分裂症）,bipolar disorder （躁郁症）and alcoholism（酗酒）,confirms a large study published in the recent issue of the British scientific journal Nature.

The world's largest study into the genetic basis of mental illnesses was led by researchers from British universities,including University College London (UCL),Cardiff University and King's College London (KCL).

Researchers believe that they are now much closer than before to understanding the complex biological causes, which make some people being at high risk of developing mental illnesses.They also believe that these findings could lead to new treatments.

The researchers analyzed the DNA of about 37,000 patients with schizophrenia,bipolar disorder or alcoholism, and compared the smallest genetic changes to those found in about 113,000 healthy people.They then identified about 128 independent genetic variants（变体）at 108 locations on the human chromosomes（染色体）that contribute significantly to developing schizophrenia—83 of these sites have never before been linked to the illness,according to scientists.

For example,people with the variant of the GRM3 gene,thought to be important in brain signaling,are around 2 to 3 times more likely to develop schizophrenia or alcohol dependence.The variant,which is found in approximately one in every 200 people,is also associated with a three times risk of developing bipolar disorder.

"We could be looking at the next big drug target for treating mental illness,"Professor David Curtis from UCL, co-author of the paper,said."The work opens up new ways to prevent and treat mental illnesses by revealing the mechanisms involved in their development."

1.What can we learn from Paragraph 3?

A. Researchers are disappointed at curing biological causes.

B. Researchers are worried about the complex biological causes.

C. Researchers have found the method of curing biological causes.

D. Researchers are confident for figuring out the complex biological causes.

2.According to Paragraph 4,the researchers found       .

A. there are 37,000 patients with mental illnesses in the world

B. most of the sites have never before been linked to mental illnesses

C. there is little difference between the patients and the healthy people

D. the cause of mental illnesses has nothing to do with the genetic changes

3.We can learn from Paragraph 5       .

A. the variant of the GRM3 gene is important

B. the number of people with the variant of the GRM3 gene is large

C. the number of people with the variant of the GRM3 gene is small

D. people with the variant of the GRM3 gene aren't likely to suffer schizophrenia

4.What's the main topic discussed in the text?

A. The importance of gene variants.

B. The research of gene variants.

C. The cause of mental illnesses.

D. Gene variants linked to mental illnesses.