Many of the world's pollution problems have been caused by the crowding of large groups of people into the cities．Supply for the needs of the people leads to further       by industry．If the rapid increase of world population continues at the present rate, there may be much greater       to human beings．
Some scientists speak of the increase in numbers of people as "population pollution''．
About 2,000 years ago, the world population was about 250 million．It        a billion in 1850．By 1930 the population was two billion．It is now six billon．It is       to double by the year 2020．If the population continues to grow at the same rate, there will be 25 billion people in the        a hundred years from now．
Man has been       the earth's resources more and more        over the past years．Some of them are almost gone．Now many people believe that man's greatest problem is how to control the        of the population．The material supplies in the world will be far from enough to        the human population if the present rate of increase continues．
There is already over-crowding in many cities and starvation in some countries．Many people believe that human survival in the future        on the answer to the question．

A．progress B．pollution C．education D．production

A．danger B．harm C．benefit D．hardship

A．got B．took C．brought D．reached

A．suggested B．hoped C．expected D．said

A．world B．country C．star D．end

A．discovering[ B．using C．digging D．destroying

A．seriously B．dangerously C．rapidly D．steadily

A．existence B．start C．growth D．birth

A．increase B．starve C．construct D．support

A．depends B．agrees C．saves D．passes