8．difficult 9．with 10．happening(stop．．．from doing)意为“阻止／防止……去做某事”)
(2)
The population
problem may be the 1 one
of the world today． The world's population is growing 2
． Two thousand
years ago, there were only 250 million people 3
the earth． Four hundred
years ago, the number was 4 500 million． But at the beginning of the 5 century,
the world's population was about 1,700 million．In 1970, this number was 3,600 million． In 1990, the number was five billion． A 6
report says that the world population will
7 six billion by the end of the
20th century． This is just
ten 8
after it 9 five
billion． People say
that by the year 2010, 1 0
may be seven billion．