果园里的桃树比杏树多40棵，杏树的棵数是桃树的80%，桃树有多少棵？

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.

58().

A. in general

B. on average

C. by contrast

D. at length

在电梯的天花板上系有一根细绳，绳的下端系一质量为10kg的铁块，细绳的质量忽略不计．已知细绳能够承受的最大拉力为120N，为使细绳不被拉断，（g取

10m

s2

）．则关于电梯的运动以下说法正确的是（　　）

A．电梯向上做减速运动时，加速度的值最大不得超过

2m

s2

B．电梯向上做加速运动时，加速度的值最大不得超过

2m

s2

C．电梯向下做减速运动时，加速度的值最大不得超过

2m

s2

D．电梯向下做加速运动时，加速度的值最大不得超过

2m

s2

早期食管癌钡餐造影分型有（）

A.斑块型

B. * * 型

C.糜烂型

D.平坦型

E.髓质型

党的地方委员会工作必须遵循的原则不包括（）

A、坚持立党为公、执政为民，认真践行党的宗旨和群众路线

B、坚持从实际出发，分类指导

C、坚持领导带头，以上率下

D、坚持民主集中制，增强党的地方委员会领导集体活力和党的团结统一

E、坚持党要管党、从严治党，始终保持党的先进性和纯洁性

活塞由顶部、（）、销座、裙部等部分组成。

A.气环

B.油环

C.防漏部

D.活塞销