The impetus(推动力) behind the research that led to Dolly was not to find a way
to clone humans but rather to develop genetically engineered animals that would
serve a variety of purposes. As there are great genetic differences in cattle
herds and sheep flocks, breeding copies of selected livestock would increase the
efficiency of agricultural productivity and help improve the quality of such
commercial products as milk, beef, and wool.
As in the management of other breeding schemes, it will be important for
scientists to maintain the balance between intense selection of livestock and
the maintenance of genetic variability. Preservation of frozen cells from a
large number of representatives of different breeds would allow nuclei from
those donor cells to be used as required. The ethical issues in animal cloning
are perhaps less controversial than with humans; nevertheless ,some people worry
that producing large numbers of animal clones only increase the likelihood that
these animals will be mistreated.
Genetic modification of livestock will also provide new opportunities in
medicine and research. Today many patients in need of transplants die before
organs become available from suitable donors. Cloning pigs has been suggested as
a means of rapidly achieving xenotransplantation (异种移植), the use of animal
organs to replace organs in human patients. Organs transplanted between species
are in er of being destroyed within minutes by the acute immune response of
the body receiving the transplant; however, strategies are being developed to
modify pigs genetically so that rejection by the immune system may be
effectively pred.
31.According to the passage people object to the use of cloning to produce
copies of humans mainly because _________.
A.its technique is not good enough
B.it is immoral and leads to wrong expectations
C.it may lead to parents' unnatural behavior. to the copy of them
D.it may lead to many people' s unemployment
32.Which of the following words can be used to replace the word "well" in
Para. 1, Line 6?
A.easily
B.as one would wish
C.quite possibly
D.skillfully
33.In breeding copies of selected livestock, scientists should take into
consideration of all the following aspects EXCEPT_________.
A.the balance between extreme selection of livestock and continuation of
genetic variability
B.ill-treatment of the copied animals
C.preservation of frozen cells
D.intense opposition to animal cloning
34.What do you think would be described in the next paragraph of the passage?
_________.
A.The strategies to modify pigs genetically.
B.People's response to the proposals above.
C.The immune system.
D.Another potential medical application of cloning.
35.What is the author's attitude towards the technique of cloning?
_________.
A.In favor of cloning both animals and humans.
B.In favor of cloning animals but not humans.
C.In favor of cloning humans but not animals.
D.In favor of neither cloning animals nor humans.