在有限经验的基础上形成的刻板印象往往具有消极的性质，会使人对某些群体的成员产生（）。

提高加氢装置氢分有那些途径？氢分压高对反应有何影响？

已知方程3（x+2）=5x（1），与4x-3（a-x）=6x-7（a-x）（2）有相同的解，则a=______．

县级以上道路运输管理机构进行道路旅客运输企业质量信誉考核时，客运企业提供的资料包括（）等。

A．企业基本情况

B．安全生产情况

C．违法行为情况

D．服务质量情况

American doctors say that mothers who smoke cigarettes before their babies are born may slow the growth of their babies’ lungs. They say reduced lung growth could cause the babies to suffer breathing problems and lung diseases later in life. Doctors in Boston studied 1,100 children. The mothers of some of the children smoked, the other mothers did not. Doctors found that the lungs of the children whose mothers smoked were 8% less developed than the lungs of the children whose mothers did not smoke, and that the children whose mother smoked developed 20% more cold and breathing diseases than other children later in life.

Another recent study found that children had a greater chance of developing lung cancer if their mothers smoked. The study also showed that the danger of lung cancer increased only for sons and not for daughters, and that the father’s smoking did not affect a child’s chance of developing lung cancer

49.  Whose baby would have breathing diseases?

A.Mother who smokes cigarettes after their baby are born

B.Mother who smokes cigarettes before their baby are born

C.Mother who don’t smoke at all

D.Mother whose mother smokes

50. Suppose John’s father was a heavy smoker, so was Mary’ mother. According to this study,  _________.

A. John is more likely to develop lung cancer                                                     B. Mary is more likely to develop lung cancer                           

C. Mary and John have the same chance to develop lung cancer              

D. Neither John and Mary has the chance to develop lung cancer      

51. This passage is to __________.

A. warn us of the danger of smoking before children.

B. warn people with breathing problems not to smoke.

C. warn us that mothers who smoke may affect their children’s health.      

D. warn us that fathers who smoke may affect their children as mothers

在回转窑煅烧系统中，物料在竖式预热器内的传热，是靠吸收气流中的热，以（）方式进行的。

A.传导传热 

B.辐射传热 

C.对流传热