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
第二大题 完形填空 (20小题, 共30分)
Pearls(珍珠) are
valuable white gems (宝物) which come from the ocean. Actually
they are 16 by oysters, small shell fish that live on
the 17 of the ocean.
18 oysters(牡蛎,蚝) 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(使…… 不适,刺激) 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.