按一对夫妇一两个孩子计算，人口学家统计和预测，墨西哥等发展中国家的人口翻一番大约20—40年，美国需要40—80年，瑞典人口将会相对稳定，德国人口将减少。预测人口的这种增减动态主要决定于（）。
A、种群数量和密度
B、种群年龄结构
C、种群性别比例
D、出生率和死亡率
相关专题： 人口学家 出生率 死亡率
相关问题推荐
B:学生倘若身陷题海无暇读书，我们就只能眼睁睁地看着朝气蓬勃的孩子变成刻板僵化的应试机器，不但失掉创新的能力，更可能拙于理性表达。
C:教育改革必须是有利于学生的终身发展、有利于基础教育、有利于大学发展的系统改革。因此，高考改革定会借助更多专家的力量，在认真研究的基础上才出台。
D:苏轼历经仕途坎坷，却始终能以旷达之心消解现实痛苦，他车富而又精彩的人生经历，正是那句流传甚广的话“生活予我以苦痛，我却报之以歌”的真实写照。
In “Relax, We’ll Be Fine”, columnist David Brooks writes, “the fact is, despite all the problems, America’s future is extremly bright.”
Mr. Brooks acknowledges that “According to recent survey, 60 percent of Americans think the country is heading in the wrong direction. The same percentage believe that the U.S. is in long-term decline. The political system is not functional. A financial crisis looks unavoidable. There are plenty of reasons to be sad.”
But, he writes:
“Demographers（人口学家) predict that over the next 40 years, the U.S. population will increase by an additional 100 million people, to 400 million over all. The population will be determined, hardworking and relatively young. In 2050, only a quarter will be over 60, compared with 31 percent in China and 41 percent in Japan.”
As the rising generation leads an economic recovery, it will also participate in a communal
（of community) one. We are living in a global age of social entrepreneurship（创业精神).
In sum, the U.S. is on the edge of a demographic, economic and social recovery, built on its historic strengths. The U.S. has always been good at destructive change. And it’s always been good at decentralized community-building, too. Surely a country with this much going for it is not going to wait around passively and let a rotten political culture drag it down.
51．In his article Relax, We’ll Be Fine, David Brooks intends to________.
A．encourage Americans to be optimistic about their future
B．give Americans courage to face their financial crisis
C．persuade Americans to live happily and generously
D．inspire Americans to lead an economic recovery
52．There are all the reasons for Americans to be unhappy except____
A．the function-failed political system B．the increasing population
C．the declining economy D．the wrong direction and financial crisis
53．Over the next 40 years, according to David Brooks, Americans will be____
A．more optimistic and humorous B．more pessimistic and stronger
C．more energetic and promising D．more considerate and aggressive
54．In the author’s opinion, America________.
A．has always benefited from wars B．has done well by its political system
C．has contributed a lot to human progress D．has contributed to world’s economy
55．We can learn from the passage that____
A．American political system and culture are backward
B．Americans are not a nation to give in to difficulties
C．Americans are very destructive and aggressive
D．America has been in an economic and social recovery
B:学生倘若身陷题海无暇读书，我们就只能眼睁睁地看着朝气蓬勃的孩子变成刻板僵化的应试机器，不但失掉创新的能力，更可能拙于理性表达。
C:被誉为中国当代最杰出科幻作品之一的小说《三体》即将被拍成电影，但它并不像美国大片《星际穿越》那样，主题偏离主流，观众接受起来有难度。
D:苏轼历经仕途坎坷，却始终能以旷达之心消解现实痛苦，他丰富而又精彩的人生经历，正是那句流传甚广的话“生活予我以苦痛，我却报之以歌”的真实写照。
A人口红利
B人口转变
C人口负债
D人口赤字
1944年，（）人口学家诺特斯坦发展的兰迪的理论，第一次提出了“人口转变”，并将兰迪的第三序列划分为三个阶段。
A、美国
B、法国
C、英国
D、日本
