消化道平滑肌对下列刺激不敏感的是

By 1870, about 45 percent of the U.S. population moved to factory towns.

A．Y

B．N

C．NG

If we want to feed the world's population in 2050, our food production needs ______.

A．to increase by 30 percent

B．an increase of 300 percent

C．to increase to 3 billion tons per year

D．an increase of three times

Section B

Directions: There are 2 passages in this section. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A, B, C and D. You should decide on the best choice.

It will come as no surprise that the earth is going to be a much more crowded place in the next century. From a global population of about 5. 4 billion today, the United Nations Fund for Population Activities says we' II see a rise to 8. 2 billion people in 2025. The U. N. expects the total population to stabilize (稳定) at Il. 6 billion sometime later in the 2000 s.

More than ninety percent of the population growth will occur in developing countries. Eighteen of the world' s twenty largest cities will be in these lands as the number of urban-dwellers (城市居民) swells from roughly two billion to 5.1 billion. The Unites States and Europe, which in 1950 accounted for twenty-two percent of the world' s population, will be home to less than nine percent of its people in 2025. By contrast, Africa' s share of the total will climb from nine percent in 1950 to nearly twenty percent by 2015. Ethiopia should double in size to almost 100 million people. In about the same time period, India will overtake China as the world' s most populous country.

For the United States, the big news won' t be an abundance of new faces; experts predict the country will grow from its present 250 million population and stabilize at about 350 million sometime before the middle of the 21st century. The important changes will be in American ethnic (种族的) makeup. Twenty years from now, the United States white, non-Hispanic majority will peak at 195 million, and then may decline in numbers. Asian-Americans will become an increasingly important minority, while African-Americans--whose population growth rate is slowing dramatically--will become the second-largest minority behind Hispanics, a half million of whom are now thought to be emigrating to the United States legally and otherwise, each year.

This article is primarily about ______.

A．population growth in developing countries

B．why the world' s population is changing

C．how the population is going to change in different parts of the world in the future

D．the sharp contrast in population changes between developing and developed countries