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阿伏加德罗常数为NAmol-1．现有某气体，它的摩尔质量是M g•mol-1，在t℃1.01×105Pa时，气体摩尔体积为Vm L•mol-1．取t℃1.01×105Pa时此气体m g，回答下列问题：

（1）该气体一个分子的质量______g；

（2）m g该气体中所含的分子数目______个；

（3）t℃1.01×105Pa时，m g该气体的体积______ L．

（4）能否用上述数据求一个该气体分子的体积？①若能，其计算式为______．

②若不能，其理由是______．

答案

（1）该气体摩尔质量是M g•mol，阿伏加德罗常数为NAmol-1．根据摩尔质量定义，该气体一个分子的质量为

Mg•mol-1
NAmol-1
=
M
NA
g．故答案为：
M
NA
g

（2）N=n×NA=

m
M
×NA=
mNA
M
个，故答案为
mNA
M
个：

（3）V=nV m=

m
M
×V m=
mVm
M
L，故答案为
mVm
M
L；

（4）②不能，因为分子的体积相对于气体的体积来说，微乎其微，决定气体体积的是分子间的平均距离，故答案为：气体分子间的平均距离大于气体分子的直径，所以气体的体积主要由气体分子间的平均距离决定．

阅读理解

What should you think about in trying to find your career（职业）? You are probably better at some school subjects than others.  1 A boy who is good at mathematics can use that in an engineering career. 2 So it is important to do well at school. On the other hand, you may not have any specially strong or weak subjects but your records show a general satisfactory standard. 3 Knowledge of history is not required for most jobs but if history is one of your good subjects you will have learned to remember facts and details. This is an ability that can be useful in many jobs.

4 If nothing else, you may have learned how to get to work on time, to follow instructions and to get on with older workers. Just as important, you may become interested in a particular industry or career you see from the inside in a part-time job.

Facing your weak points is also part of knowing yourself. 5 Your school record, for instance, may not be too good, yet it is an important part of your background. You should not be apologetic about it but instead recognize that you will have a chance of a fresh start at work.

A．He may do well in his future work.

B．It is better to face any weaknesses than to pretend they do not exist.

C．Although not all subjects can be used directly in a job, they may have indirect value.

D．These may show strengths（优势） that you can use in your work.E. Your school must have taught you the skills.

F. A girl who spells well and likes English may be good at office work.

G. If you have had a part-time job on Saturday or in the summer, think what you gained from it.
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单项选择题

该企业2003年境外所得允许抵扣的所得税为( )万元。

A．39.6

B．36

C．20

D．26
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