为了用实验的方法验证镁和铁的金属性强弱,学生甲和学生乙分别设计了两种不同的方法:

题型:问答题

问题:

为了用实验的方法验证镁和铁的金属性强弱,学生甲和学生乙分别设计了两种不同的方法:

方案一:学生甲用水作试剂,比较镁和铁与水反应的情况

方案二:学生乙用稀盐酸作试剂,比较镁和铁与稀盐酸反应的情况

回答下列问题:

(1)以上两实验方案实验现象较为明显的是方案______

(2)学生乙在实验中取了一段镁条,投入稀盐酸中,现象不是十分明显,请分析原因______.

(3)学生丙另辟蹊径,仅用镁条、铁片与盐酸只进行一次实验也得出正确的结论(其它用品自选),学生丙用的是什么方法?______简述现象______.

考点:实验操作达到的预期目的
题型:问答题

被称为世界电影之都的是:[ ]

A、巴黎

B、维也纳

C、西安

D、好莱坞

题型:问答题

全心衰竭出现的发绀属于()。

A.缺血性发绀

B.心性混血性发绀

C.肺性发绀

D.淤血性发绀

E.混合性发绀

题型:问答题

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 (91) on the individual suggest that children engage in criminal behavior (92) they were not sufficiently penalized for previous misdeeds or that they have learned criminal behavior through (93) with others. Theories focusing on the role of society suggest that children commit crimes in (94) to their failure to rise above their socioeconomic status, (95) as a rejection of middle, class values.
Most theories of juvenile delinquency have focused on children from disadvantaged families, (96) the fact that children from wealthy homes also commit crimes. The latter may commit crimes (97) lack of adequate parental control. All theories, however, are tentative and are (98) to criticism.
Changes in the social structure may indirectly (99) juvenile crime rates. For example, changes in the economy that (100) to fewer job opportunities for youth and rising unemployment (101) make gainful employment increasingly difficult to obtain. The resulting discontent may in (102) lead more youths into criminal behavior.
Families have also (103) changes these years. More families consist of one-parent households or two working parents; (104) , children are likely to have less supervision at home (105) was common in the traditional family (106) . This lack of parental supervision is thought to be an influence on juvenile crime rates. Other (107) causes of offensive acts include frustration or failure in school, the increased (108) of drugs and alcohol, and the growing (109) of child abuse and child neglect. All these conditions tend to increase the probability of a child committing a criminal act, (110) a direct causal relationship has not yet been established.

A.incidence

B.awareness

C.exposure

D.popularity

题型:问答题

破伤风病人的主要致死原因是()

A.水、电解质平衡紊乱

B.肺部感染

C.呼吸困难、窒息

D.酸中毒

E.心肌抑制

题型:问答题

下列叙述错误的是()

A.脱氧核糖、葡萄糖、核糖既存在于植物细胞内,又存在于动物细胞内

B.细胞体积越大,相对表面积越大,细胞的物质运输效率就越高

C.代谢活动旺盛的细胞中自由水相对含量较多

D.染色体、噬菌体都是由核酸和蛋白质组成的

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