Many theories concerning the causes of juvenile delinquency (crimes committed by young people) focus either on the individual or on society as the major contributing influence. Theories 　1　on the individual suggest that children engage in criminal behavior 　2　they were not sufficiently penalized for previous misdeeds or that they have learned criminal behavior through 　3　with others. Theories focusing on the role of society suggest that children commit crimes in 　4　to their failure to rise above their socioeconomic status 　5　as a rejection of middle-class values.
　　Most theories of juvenile delinquency have focused on children from disadvantaged families, 　6　the fact that children from wealthy homes also commit crimes. The latter may commit crimes 　7　lack of adequate parental control. All theories, however, are tentative and are 　8　to criticism.
　　Changes in the social structure may indirectly 　9　juvenile crime rates. For example, changes in the economy that 　10　to fewer job opportunities for youth and rising unemployment 　11　make gainful employment increasingly difficult to obtain. The resulting discontent may in 　12　lead more youths into criminal behavior.
　　Families have also 　13　changes these years. More families consist of one-parent households or two working parents; 　14　, children are likely to have less supervision at home 　15　was common in the traditional family 　16　. This lack of parental supervision is thought to be an influence on juvenile crime rates. Other 　17　causes of offensive acts include frustration or failure in school, the increased 　18　of drugs and alcohol, and the growing 　19　of child abuse and child neglect. All these conditions tend to increase the probability of a child committing a criminal act, 　20　 a direct causal relationship has not yet been established.

______

A.survived 

B.noticed 

C.undertaken 

D.experienced