海运提单之所以能够向银行办理抵押贷款，是因为（） A.海运提单是承运人签发的货物收据

British and American scientists are raising genetically modified(转基因的) pigs in the hope of providing organs for transplant(移植) to humans, the project leader wrote in a newspaper Sunday.
Scientists in London and California have begun conducting the genetic experiments to find a solution to record–long waiting lists for organ transplants, Robert Winston said in an opinion piece written for Britain's Sunday Times.
In Britain alone, around 8,000 patients are waiting for a transplant.
"People needing a new heart or liver are waiting for someone else to die – usually a violent death in a traffic accident," Winston wrote in the newspaper. He said his team was "trying to modify pigs so their organs might save the lives of humans."
The scientists are introducing human genes into the animals to reduce the chances of the organs being rejected by patients, as has been common in previous attempts to use animal tissues, said Winston, who heads the Institute of Reproductive and Developmental Biology at London's Hammersmith Hospital.
Working with Dr. Carol Redhead of the California Institute of Technology, Winston's team has injected human genes directly into male piglets(猪仔), adding them to the animal's sperm(精子).
He said that pigs involved in experiments had successfully produced transgenic sperm, but acknowledged that British and European laws had prevented the team from using the pigs to mate.
The Sunday Times newspaper reported that the experiments would be moved to the United States following difficulties with funding and regulations in Britain. It said the pigs would be bred in Missouri.
"Our U.S. friends will benefit from our technology and the income we might have produced for Britain will be lost," Winston wrote.
Some scientists have previously blamed the idea of using animal organs for human transplant, saying the technique risks spreading animal viruses to humans. Winston said his research project is attempting to breed virus-free pigs.
49. Scientists are introducing human genes into the animals to ____________.

A. make the organs healthier	B. reduce the pain of animals
C. make the organs live longer	D. reduce the chances of rejection

50. Some scientists have blamed the idea of using animal organs for human transplant because ____________.

A. the technique is not perfect now

B. humans may be infected with animal viruses

C. it is against laws and regulations

D. it may cause a conflict between humans and animals

51. According to Winston, it seems ___________ to Britain to move the experiments to the United States.            

A. a pity

B. a pride

C. a disaster

D. a good idea

52. It can be inferred from the passage that ____________.

A. animal organs are commonly used for human transplant now

B. lots of patients need animal organ transplants now

C. examples of the animal tissues being rejected have happened

D. it is not safe to use animal organs for human transplant