单选题
Dolly was once an awfully lonely sheep．When the
famous cloned (of an exact copy of a plant or animal made by taking a cell from
it and developing it artificially) animal made headlines in 1997，she was the
only mammal ever to be manufactured from the cell of an adult donor．Since
then，the clone ranks have swelled，with mice and cattle also making their way out
of the labs．Last week cloning technology took another step forward when an
international biotechnology company announced that it had created a litter of
five genetically identical piglets (young pigs)，and that it had a pretty good
idea of how they could one day be used：as organ donors for ailing
humans． The idea of turning pigs into tissue factories has been
around for at least 30 years．Pigs breed easily and mature quickly，and their
organs are roughly the same size as those of humans，meaning operations can be
performed with a relative snap-out，snap-in simplicity．The problem is，once the
donor organ is stitched in place，the body rebels，rejecting it even more
violently than it would a human transplant．“A pig heart transplanted in a person
would turn black within minutes．” says David Ayares，a research director with PPL
Therapeutics，the biotech firm that helped clone Dolly and also produced the
piglets． What causes pig organs to be rejected so quickly is a
sugar molecule on the surface of pig cells that identifies the tissue as
unmistakably nonhuman．When the immune system spots this marker，it calls out its
defenses．PPL scientists recently succeeded in finding the gene responsible for
the sugar and knocking it out of the nucleus of a pig cell．Their next step would
be to extract that nucleus，insert it into a pig ovum，and then into the womb of a
host pig．The sugar free piglet that was eventually born could then be cloned
over and over as a source of safe transplant organs．The idea is to arrive at the
ideal animal and repeatedly copy it exactly as it is．The cloned piglets PPL
introduced to the world last week were created in just this way，though for this
first experiment in pig replication the scientists left the sugar genes
intact． Despite this recent success，PPL is not likely to be
setting up its organ shop anytime soon．Knocking out the key sugar gene solves
only the problem of short-term rejection．Much more has to be done before any
solution to long-term rejection can be rotund．Nonetheless，Ayares is
optimistic，insisting that pig organs could be available in as little as five
years．For the present，even a little new transplant material is a big improvement
over what’s available，and for gravely ill patients awaiting a donor，that’s no
small thing．
单选题
What is true about Dolly according to the text？
A. She was a lonely sheep in the first place．
B. She was manufactured out of the lab．
C. She was cloned from the cell of a mature sheep．
D. She was replaced by cloned piglets in terms of importance．
【正确答案】
C
【答案解析】[解析] 细节题，参见文章第二句话后半句…she was the only mammal ever to be manufactured from the cell of an adult donor．其大意是：她是唯一一个由成年原体提取的细胞培养而成的哺乳动物。此处的adult donor即指代C中所说mature sheep，故正确答案为C。
单选题
The“tissue factories”in the second paragraph most probably refers
to______．
A. the five genetically identical piglets．
B. places for the production of tissues．
C. animals whose organs would be used for human consumption．
D. animals which would be raised in quantity for transplant
materials．
【正确答案】
D
【答案解析】[解析] 词汇题，参见文章第2段：The idea of turning pigs into tissue factories has been around for at least 30 years．Pigs breed easily and mature quickly，and their organs are roughly the same size as those of humans，meaning operations can be performed with a relative snap-out，snap-in simplicity．其大意是：把猪当作“器官组织工厂”这个想法已经存在至少30年了。猪很容易饲养并且成熟得很快，它们的器官大小和人体的差不多，这就意味着进行移植手术相对容易。由此可知，此处的“器官组织工厂”指的是为获取移植器官组织而大量繁殖的动物，故正确答案为D。
单选题
One problem of using pig organs on humans is______．
A. the size of the pig organs．
B. the quick rejection of the transplant by human bodies．
C. the speed of their maturity．
D. the technical complexity of the operational process．
【正确答案】
B
【答案解析】[解析] 细节题，参见文章第2段第3句：The problem is，once the donor or-gan is stitched in place，the body rebels，rejecting it even more violently than it would a human transplant．其大意是：问题是，移植后人体会立刻产生排异反应，且反应要比植入人的器官要强烈的多。以及后面的“A pig heart transplanted in a person would turn black within minutes”(猪心脏如果植入人体内的话，会在几分钟之内变黑)。由此可知，猪的器官植入人体后很快就会起排异反应。故正确答案为B。
单选题
PPL scientists will try to solve their problem by______．
A. removing the sugar molecule on the surface of pig cells．
B. distinguishing human tissues from those of pigs．
C. using the sugar-free nucleus in cloning a pig．
D. taking out the sugar genes from the cell of a pig．