问题
选择题
元素周期律和元素周期表是学习 化学的重要工具，下列叙述不正确的是 [ ]
A．从左到右，元素周期表中的第15列为VA族
B．某ⅡA族元素的原子序数为x，则与它同周期的ⅢA族元素的原子序数可能为x+25
C．ⅥA族元素，随原子半径增大，对应气态氢化物的稳定性逐渐增强
D．53号元素位于周期表中第5周期ⅦA族
答案
答案：C
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元素周期律和元素周期表是学习 化学的重要工具，下列叙述不正确的是 [ ]
A．从左到右，元素周期表中的第15列为VA族
B．某ⅡA族元素的原子序数为x，则与它同周期的ⅢA族元素的原子序数可能为x+25
C．ⅥA族元素，随原子半径增大，对应气态氢化物的稳定性逐渐增强
D．53号元素位于周期表中第5周期ⅦA族
答案：C
| The first 50 years of the next millennium will be critical for the world’s population. By 2050 population growth should have leveled off, but by then we’ll have 10 billion people -- two-thirds as many again as we have today. The rate of population growth is something we can choose right now, though it’s not something that just happens, but a matter of human choice. The choice is a complicated one, with many variables, but it remains a choice. If we want to prevent a population explosion, we should take action now -- or assist the poorer countries to do so. They need better government, better institutions, better labor and capital markets, better schools. Anything that increases the value of women’s time and adds to the cost of caring for a child makes a woman less likely to have that child. Since big families are often seen as safety nets for illness and old age, improving poor people’s access to insurance, pensions and welfare institutions also has a major impact. This can be as simple as rural credit, providing a means of saving. Finally, there is education -- both for women and, perhaps even more important, for the next generation of children. These steps are there to be taken, but there appear to be some countries that are not seriously trying at the moment. If we cannot achieve that we will certainly not control population. That said, I don’t feel pessimistic that we are going to run out of resources: we are becoming more efficient at producing food faster than the rate at which population is increasing. There is, however, a risk that we will wreck the environment so effectively that the world will no longer be an attractive place to live. That really would be a dismal outcome, to reach world population equilibrium only to find we’d destroyed the natural environment in the process. |
The author is more worried about the ______.
A．shortage of food in the future
B．illiteracy of the people
C．welfare of the poor people who have more children
D．the damage of the surroundings in which we live