Ⅰ.完形填空
Pearls (珍珠) are valuable white gems (宝物) which come from the ocean.Actually they are 1 by oysters (牡蛎，蚝) ，small shell fish that live on the 2 of the ocean.
3 oysters will make pearls; not all oysters produce them.Oysters produce pearls only when they are 4 by sand.If a 5 of sand enters the oyster's 6 ，the oyster becomes hurt because the 7 grain of sand irritates (使……不适，刺激) the smooth, soft skin of the oyster.The oyster tries to 8 itself by producing a white 9 that looks like milk.The oyster covers the 10 with the milky fluid.The fluid protects the oyster.Later the white liquid becomes 11 .This hardened liquid forms a shell, or bead, around the sand.At this time a pearl is beginning to 12 .
The white pearl grows 13 inside the oyster's shell. 14 ， it takes about six or seven years for the oyster to produce a pearl.Not all oysters produce pearls 15 most oysters sometimes take sand into their 16 .Only sand which the oyster cannot get rid of will 17 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 18 ，then it will produce the white fluid to 19 itself.Actually, only about one in a thousand oysters will produce a pearl；that is， 20 than one percent.
本文介绍了牡蛎制造珍珠的详细过程。
1．A.invented B．brought
C．produced D．caused
答案：C
解析：produce“生产”，根据下文“not all oysters produce them”可知C项正确。
2．A.bottom B．base
C．surface D．ground
答案：A
解析：根据下文“Oysters produce pearls only when they are 4 by sand.”可知牡蛎生活在海底。
3．A.Only some B．Only few
C．All of D．A lot of
答案：A
解析：根据下文“not all oysters produce them”可知“不是所有的牡蛎都产珍珠，只有一些能产”。
4．A.harmed B．covered
C．destroyed D．injured
答案：B
解析：根据上下文的逻辑关系可知，牡蛎被沙子覆盖导致沙子进入牡蛎壳内，这时牡蛎才会产珍珠。
5．A.piece B．grain
C．little D．bit
答案：B
解析：a grain of sand“一粒沙子”。
6．A.shell B．body
C．eyes D．back
答案：A
解析：沙子首先进入牡蛎的壳内。
7．A.hard B．vivid
C．sharp D．rough
答案：D
解析：上文说牡蛎受到伤害，可见沙子是粗糙的。
8．A.prevent B．preserve
C．protect D．guard
答案：C
解析：protect“保护”。牡蛎是为了保护自己才产生一种白色的液体。
9．A.water B．matter
C．liquid D．object
答案：C
解析：根据空格后的“that looks like milk”可知牡蛎产生的东西是一种液体。
10．A.injury B．shell
C．sand D．pearl
答案：C
解析：因为沙子伤害了自己的身体，所以牡蛎产生的“the milky fluid”是把沙子盖住。
11．A.bright B．hard
C．strong D．pure
答案：B
解析：根据下文“This hardened liquid forms a shell”可知白色液体随后会变硬。
12．A.make B．produce
C．do D．form
答案：D
解析：form“形成”。指此时珍珠开始形成。
13．A.slowly B．fast
C．safely D．quickly
答案：A
解析：根据下文“it takes about six or seven years for the oyster to produce a pearl”可知珍珠生长过程是缓慢的。
14．A.Often B．Actually
C．Usually D．Sometimes
答案：C
解析：usually“通常”。此处指珍珠通常的形成期为6到7年。
15．A.even though B．in case
C．so long as D．only if
答案：A
解析：even though“即使”。尽管大多数的牡蛎壳内有时会进沙子，但是并非所有壳内进沙子的牡蛎都产珍珠。
16．A.bodies B．shells
C．bottoms D．caves
答案：B
解析：根据第6处所在句说牡蛎壳内进沙子后导致珍珠的形成可知此处也是牡蛎的壳内进沙子。
17．A.destroy B．irritate
C．soft D．open
答案：B
解析：irritate“刺激，使……不适应”。此处指“只有牡蛎摆脱不掉的沙子才能刺激它”。
18．A.sand B．shell
C．milk D．liquid
答案：A
解析：根据上文“if an oyster ‘swallows’some sand”可知，牡蛎想摆脱掉的也是沙子。
19．A.cover B．destroy
C．produce D．protect
答案：D
解析：根据上文可知牡蛎产生的“the white fluid”是起保护作用的。
20．A.fewer B．more
C．less D．smaller
答案：C
解析：根据“one in a thousand”可知概率不到百分之一，less than one percent“不到百分之一”，less than表示“少于”。
