问题 填空题

乙烯具有促进果实成熟的作用,还是合成纤维、橡胶、塑料的基本化工原料。乙烯无色,不溶于水,密度比空气小,化学式为C2H4,容易燃烧生成二氧化碳和水,与空气混合形成的混合物遇明火有引起燃烧爆炸的危险。

(1)请根据所给乙烯的化学式,写出其表示意义(写出两点即可):①__________;②_________。

(2)写出乙烯燃烧的化学方程式_________________。

(3)根据乙烯的化学性质,在生产、运输、贮存乙烯时应注意_________________。

答案

(1)①表示乙烯这种物质;②表示乙烯是由碳、氢两种元素组成的;③表示一个乙烯分子;④表示乙烯分子是由碳、氢两种原子构成的;⑤表示一个乙烯分子是由2个碳原子和4个氢原子构成的

(2)C2H4+3O22CO2+2H2O

(3)严禁烟火

单项选择题
单项选择题

"Congratulations, Mr. Jones, it’s a girl. "

Fatherhood is going to have a different meaning and bring forth a different answer from every man who hears these words. Some feel proud when they receive the news, while others worry, wondering whether they will be good fathers. Although there are some men who like children and may have had considerable experience with them, others do not particularly care for children and spend little time with them. Many fathers and mothers have been planning and looking forward to children for some time. For other couples, pregnancy was an accident that both husband and wife have accepted willingly or unwillingly.

Whatever the reaction to the birth of a child, it is obvious that the change from the role of husband to that of father is a difficult task. Yet, unfortunately, few attempts have been made to educate fathers in this re-socialization process. Although many good books have been written about American mothers, only recently have some books discussed the role of a father.

It is argued by some writers that the transition to the father’s role, although difficult, is not nearly as great as the transition the wife must make to the mother’s role. The mother’s role seems to require a complete transformation of daily routine and adaptation to a new life, on the other hand, the father’s role is less demanding and immediate. However, even though we have mentioned the fact that growing numbers of women are working outside the home, the father is still thought by many as the breadwinner in the household.

It is stated in the passage that()

A. some parents are not prepared to have a child

B. young couples do not like children at all

C. working couples do not have much time to take care of their children

D. many parents look forward to having a boy as their first child