单选题 Scientists have agreed that there is a kind of gene which results in people's violence who were ill-treated in their childhood. This could help to explain why some people who once suffered from miserable childhood are able to lead normal life while others become violent. But another argument was raised.
It was reported that one form of a gene in people's brain made it more likely for them to turn to violence—but only when they have undergone cruelty in their childhood. The researchers collected the life histories of 420 boys, all of whom were born in Los Angles in 1980. Among them, 145 boys had been maltreated in their first 8 years and 29 were badly ill-treated. Among the 145 kids, 49 had a less active variant(变异体) of a gene and 96 had this more active variant. The probability of those 49 boys being in difficulty is twice as much as that of the other group.
Prof. Williams believes that up to now a "violence" gene has not been discovered. Boys with the less active variant not maltreated during their childhood can have normal lives. " It is a very common phenomenon. One-fourth to one-third of us have this variant," he said, "So the gene doesn't make much difference. It doesn't lead to any trouble unless we are abused. "
The gene may show the capability of tolerating mental pressure as well. However, the discovery brings about the argument that people with the less active variant can be great dangers to our society. "This research will easily cause people to solve social issues with the help of medical treatment." said David Johnson of the USA Gene Association.

单选题 Scientists believed that ______.
A. some gene plays an important role in human beings
B. people with sad childhood will become violent
C. one kind of gene is the most important in human body
D. some gene functions partly in violence in men with miserable childhood

单选题 From the passage we can know the less active variant of the gene ______.
A. will determine men's personality and behaviour
B. always result in trouble-making
C. plays no role in children's development
D. may be responsible for boys' bad deeds

单选题 We can learn that those men who have stronger capability of tolerating mental pressure usually ______.
A. have the less active variant of gene
B. have the more active variant of the gene
C. had maltreated childhood
D. had no maltreated childhood

单选题 We can infer from the passage that ______.
A. one-fourth to one-third of the population carry the less active variant
B. children with the less active variant will not turn to normal lives
C. the less active variant and ill-treated experience lead to violence
D. all the people agree to the idea of "violence" gene

单选题 David Jackson's words in the last paragraph imply that ______.
A. he thinks the findings to solve the social problems too simple
B. he doesn't believe the possible role of the less active variant
C. he agrees to the research findings of the gene MAOA
D. he considers that the research is significant