大跨度水、旱假山洞顶面有时用钢筋混凝土配置补强，其厚度一般不应超过20cm，否则结顶

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 (51) on the individual suggest that children engage in criminal behavior (52) they were not sufficiently penalized for previous misdeeds or that they have learned criminal behavior through (53) with others. Theories focusing on the role of society suggest that children commit crimes in response to their failure to rise above their socioeconomic status, (54) as a rejection of middle-class values. Most theories of juvenile delinquency have focused on children from disadvantaged families, ignoring the fact that children from wealthy homes also commit crimes. The latter may commit crimes (55) lack of adequate parental control. All theories, however, are tentative and are (56) to criticism. Changes in the social structure may indirectly (57) juvenile crime rates. For example, changes in the economy that lead to fewer job opportunities for youth and rising unemployment (58) make gainful employment increasingly difficult to obtain. The resulting discontent may in turn lead more youths into criminal behavior. Families have also (59) changes these years. More families consist of one-parent households or two working parents; consequently, children are likely to have less supervision at home (60) was common in the traditional family structure. This lack of parental supervision is thought to be an influence on juvenile crime rates.

55().

A.on 

B.in 

C.for 

D.with

天然油脂性基质为（）

A．甘油明胶 

B．聚乙二醇 

C．液体石蜡 

D．可可豆脂 

E．半合成椰子油酯

金属油罐安装后应进行的试验包括( )。

A．焊缝质量检验

B．严密性试验

C．水压试验

D．充水试验

Only by ______ your attention ______ what you are learning can you learn it well.

A．focus；on

B．pay；on

C．focusing；on

D．paying；on

目前认为扩张型心肌病最主要的病因是（）

A.单基因显性遗传

B.持续病毒感染

C.冠状动脉病变

D.药物因素

E.心肌能量代谢障碍