20．Most people around the world are right-handed．This also seems to be true in history．In 1799，scientists studied works of art made at different times from 1，500B．C．to the 1950s．Most of the people shown in these works are right-handed，so the scientists guessed that right-handedness has always been common through history．Today，only about 10% to 15% of the world's population is left-handed．
Why are there more right-handed people than left-handed ones？Scientists now know that a person's two hands each have their own jobs．For most people，the left hand is used to find things or hold things．The right hand is used to work with things．This is because of the different work of the two sides of the brain．The right side of the brain，which makes a person's hands and eyes work together，controls the left hand．The left-side of the brain，which controls the right hand，is the centre for thinking and doing problems．These findings show that more artists should be left-handed，and studies have found that left-handedness is twice as common among artists as among people in other jobs．
No one really knows what makes a person become right-handed instead of left-handed．Scientists have found that almost 40% of the people become left-handed because their main brain is damaged when they are born．However，this doesn't happen to everyone，so scientists guess there must be another reason why people become left-handed．One idea is that people usually get right-handed from their parents．If a person does not receive the gene（基因） for right-handedness，he/she may become either right-handed or left-handed according to the chance and the people they work or live with．
Though right-handedness is more common than left-handedness，people no longer think left-handed people are strange or unusual．A long time ago，left-handed children were made to use their right hands like other children，but today they don't have to．
29．After studying works of art made at different times in history，the scientists foundC．
A．the art began from 1，500B．C．
B．the works of art ended in the 1950s
C．most people shown in the works of art are right-handed
D．most people shown in the works of art are left-handed
30．How many people in the world are left-handed now？A
A．Less than one sixth．
B．More than a half．
C．About 40%．
D．The passage doesn't tell us．
31．What is the hand for most people used to do？A
A．It's used to find or hold things．
B．It's used to work with things．
C．It's used to make a person's eyes work together．
D．It's the centre for thinking and doing problems．
32．According to the passage，which of the following is NOT true？B
A．No one really knows what makes a person become right-handed．
B．Left-handedness is cleverer than right-handedness．
C．Today children are not made to use their right hands only．
D．Scientists think there must be some reason why people become left-handed．
分析 本文主要讨论的是左撇子还是使用右手的话题，从古到今，从科学到一般的看法，作者都做了详细地阐述．
解答 29-32 CAAB
29．C 细节理解题．根据第一段2，3行In 1799，scientists studied works of art made at different times from 1，500 B．C．to the 1950s．Most of the people shown in these works are right-handed可知，在1799年，科学家们研究在不同时期从公元前1500年到20世纪50年代创作的艺术作品，在这些作品中的大部分人是右撇子．故选C．
30．A．细节理解题．根据第一段最后一句Today，only about 10% to 15% of the world's population is left-handed．可知，现在世界人口中有10%-15%的人是 left-handed，那么与此数接近的应该是 less than one sixth（不到六分之一）．故选A．
31．A．细节理解题．根据第二段For most people，the left hand is used to find things or hold things可知，对于大多数人来说，左手是用来找东西或拿东西的．故选A．
32．B．细节理解题．根据文章第三段No one really knows what makes a person become right-handed instead of left-handed．说明A正确，A long time ago，left-handed children were made to use their right hands like other children，but today they don't have to．说明C正确．so scientists guess there must be another reason why people become left-handed．说明D正确．唯独文章没有提到左撇子比使用右手的人更聪明，故B项错误．
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