题目内容：
A few years ago it was fashionable( 流行的)to speak of a generation gap, a division betweenyoung people and their elders. Parents complained (抱怨)that children did not show them proper re-spect and obedience (服从), while children complained that their parents did not understand them atall. What had gone wrong? Why had the generation gap suddenly appeared? Actually ,the generationgap has been around for a long time. Many critics argue that it is built into the fabric(结构) of oursociety. One important cause of the generation gap is the opportunity(机会)that young people have tochoose their own life style(方式)．In more traditional(传统的)societies，when children grow up，they are expected to live in the same area as their parents，to marry people that their parents knowand approve of，and often to continue the family occupation(职业)．In our society，young peopleoften traveling great distances for their educations move out of the family home at an early age，marryor live with people whom their parents have never met，and choose occupations different from those oftheir parents．
In our upwardly mobile(流动的)society，parents often expect their children to be better thanthey did：to find better jobs，to make more money，and to do all the things that they were unable todo．Often，however，the ambitions(抱负)that parents have for their children are another cause of thedivision between them．Often they discover that they have very little in common with each other．
Finally，the speed at which changes take place in our society is another cause of the gap be —tween the generations．In a traditional culture，elderly people are valued for their wisdom，but in oursociety the knowledge of a lifetime may become out of date overnight．The young and the old seem tolive in two very different worlds，separated by different skills and abilities．
No doubt，the generation gap will continue to be a feature(特征)of American life for some timeto come．Its causes are rooted in the freedoms and opportunities of our society，and in the rapid pace(速度)at which society changes．
根据以上内容,回答题.
（ ） The main idea of Paragraph l is that__________． A．the generation gap suddenly appeared
B．the generation gap is a feature of American life
C．how people can reduce the generation gap
D．many critics argue over the nature of the generation gap
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答案解析：