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

µÚ¶þ´óÌâ¡¡ ÍêÐÎÌî¿Õ (20СÌ⣬ ¹²30·Ö)

Pearls(ÕäÖé) are valuable white gems (±¦Îï) which come from the ocean. Actually they are ¡¡16 ¡¡by oysters, small shell fish that live on the¡¡ ¡¡17¡¡ ¡¡of the ocean.

18 ¡¡oysters(ĵòã¬òº) 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(ʹ¡­¡­ ²»ÊÊ£¬´Ì¼¤) 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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