完形填空。 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 l, 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, __ 10 __ may be seven billion. (    ) 1.  A. great (    ) 2.  A. faster and faster (    ) 3.  A. in (    ) 4.  A. hardly (    ) 5.  A. twenty (    ) 6.  A. USA (    ) 7.  A. past (    ) 8.  A. weeks (    ) 9.  A. get (    ) 10. A. this B. greater B. fast and falt B. on B. more B. twelve B. UN B. pass B. months B. gets B. its C. greatest C. fastest and fastest C. at C. almost C. twentieth C. PRC C. passed C. seasons C. reached C. one D. greating D. faster and fast D. for D. over D. twelfth D. PLA D. passes D. years D. reach D. it