题目内容：

    People who grow up left-handed have a different, more flexible brain structure than those born to take life by the right hand, say researchers at the University of California, Los Angeles.

The reason is that right-handers have genes that force their brains into a slightly more one-sided structure, according to the research. Left-handers appear to be missing those genes.

"There really is a difference in brains that results in a more symmetric (对称的) brain in left-handers, where the two sides are more equal," said Daniel Geschwind, who led the research team.

In the effort to understand how the brain shapes the mind, researchers have been trying to document the way genes and environment affect intelligence and mental abilities. They found that right-and left-handedness is determined by genetics. If a person has the gene for right-handedness, that person will be right-handed. People who do not have that gene, however, can be either left- or right-handed. There is no specific gene for left-handedness.

Right-handers typically have a larger left brain, where their language abilities are concentrated. Conversely, left-handers have more balanced brains. The language abilities of left-handers more often, are concentrated on the right side.

The UCLA researchers conducted brain scans on 72 pairs of male identical (同卵双生的) twins between 75 and 85 years old. They noticed that if identical twins carry the gene for hand preference, both must be right-handed. If they lack the gene, one twin can develop right-handed while the other can develop left- handed.

The researchers found that the brains of identical right-handed twins were very similar in size and structure. But when a left-hander was part of the twin set, the brains were different. The conclusion, researchers said, is that the absence of the gene for hand preference allows the brain to develop differently as the individual grows up.

1.What is the finding of the researchers of UCLA?

A.Left-handers have more balanced brains. B.Right-handers have more flexible brains.

C.Left-handers' brains are more one- sided. D.Right-handers' brains are more symmetric.

2.Which element determines a person's hand preference?

A.Environment. B.Intelligence.

C.Habit. D.Gene.

3.What can be said about identical twins?

A.They always have similar brain structure.

B.They never carry the gene for hand preference.

C.They have different genes for hand preference.

D.They can have different hand preference.

4.What did the UCLA team research on?

A.People's genetic makeup. B.People's hand preference.

C.People's brain sizes. D.People's communicative skills.