问题 选择题

设阿伏加德罗常数的值为NA,下列说法中正确的是(   )

A.1mol苯乙烯中含有的C==C数为4NA

B.2.8g乙烯和丙烯的混合气体中所含碳原子数为0.2NA

C.0.1molCnH2n+2中含有的C-C键数为0.1nNA

D.标准状况下,2.24LCCl4含有的分子数为0.1NA

答案

答案:B

苯乙烯中含有1个碳碳双键,A不正确。乙烯和丙烯的最简式都是CH2,所以B正确。烷烃中碳碳单键的数目是碳原子数减去1,即n-1,C不正确。标准状况下,四氯化碳是液体,D不正确。所以答案选B。

选择题
填空题

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

     When we think about happiness, we usually think of something extraordinary, a pinnacle (顶点) of sheer

(纯粹的) delight. And those pinnacles seem to get rarer the older we get. 

     1_____ I remember playing police and robbers in the woods, getting a speaking part in the school play.

Of course, kids also experience lows, but their delight at such peaks of pleasure as winning a race or getting

a new bike is unreserved.

     For teenagers, or people under 20 the concept of happiness changes. 2_____ I can still feel the pain of

not being invited to a party that almost everyone else was going to. I also remember the great happiness of

being invited at another event to dance with a very handsome young man.

     In adulthood the things that bring great joy-birth, love, marriage-also bring responsibility and the risk of

loss. 3_____ For Mulls, happiness is complex. 

     4_____ But I think a better definition (定义) of happiness is "the ability to enjoy something". The more

we can enjoy what we have, the happier we are. It's easy to overlook the pleasure we get from loving and

being loved, the company of friends, the freedom to live where we please, even good health.

     While happiness may be more complex for us, the solution is the same as ever. Happiness isn't about

what happens to us; it's the ability to find a positive for every negative (否定), and view a difficulty as a

challenge. 5_____

A. Love may not last; loved ones die.

B. For a child, happiness has a magic quality.

C. Happiness is the meaning and the purpose of life.

D. Being happy doesn't mean that everything is perfect.

E. The dictionary defines "happy" as "lucky" or "fortunate".

F. It's not wishing for what we don't have, but enjoying what we do possess.

G. Suddenly it's conditional on such things as excitement, love, and popularity.