16.  A. invented            B. brought               C. produced            D. caused 17.  A. bottom             B. base                 C. floor                D. ground 18.  A. Only some          B. Only few             C. All of               D. A lot of 19.  A. harmed             B. covered               C. destroyed            D. injured 20.  A. piece               B. grain                 C. little                D. bit 21.  A. shell               B. body                 C. eyes                D. back 22.  A. hard               B. vivid                 C. sharp               D. rough 23.  A. prevent             B. defend               C. protect              D. guard 24.  A. water              B. matter                C. liquid               D. object 25.  A. injury              B. shell                 C. sand                D. pearl

15. _________ from other continents for millions of years, Australia has many plants and animals not found in any other country in the world.

     A. Being separated        B. Having separated

     C. Having been separated      D. To be separated

及屈寄籾  頼侘野腎 (20弌籾�� 慌30蛍)

Pearls(寇帷) are valuable white gems (右麗) which come from the ocean. Actually they are  16  by oysters, small shell fish that live on the   17   of the ocean.

18  oysters(諜鮹��鮑) will make pearls; not all oysters produce them. Oysters produce pearls only when they are  19   by sand. If a  20  of sand enters the oyster's  21   , the oyster becomes hurt because the  22  grain of sand irritates(聞´´ 音癖��缶爾) the smooth, soft skin of the oyster. The oyster tries to     23  itself by producing a white   24  that looks like milk. The oyster covers the  25  with a milky fluid. The fluid protects the oyster. Later the white liquid become  26  . This hardened liquid forms a shell, or bead, around the sand. At this time a pearl is beginning to  27   .

The white pearl grows  28  inside the oyster's shell.  29  , it takes about six or seven years for the oyster to produce a pearl. Not all oysters produce pearls  30  most oysters sometimes take sand into their  31  . Only sand which the oyster cannot get rid of will  32  it. In other words, if an oyster "swallows" some sand, it will manage to "spit it out". If the oyster cannot get rid of the  33  , then it will produce the white fluid to  34   itself. Actually, only about one in a thousand oysters will produce a pearl; that is,  35   than one percent.

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