根据以下资料，回答题： Every yea-考呗网题库移动版

单选题根据以下资料，回答题：
        Every year, 2,000 American lives are saved by the selflessness of others．These are the bone marrow donorswho give the gift of life to patients fighting deadly diseases such as leukemia, lymphoma, and aplastic anemia．That's the good news．The bad news is that thousands more die each year because not enough people have signedon to the registries that would help the ill find a suitable match for a transplant．
        Bone marrow or stem-cell transplants are usually a last resort, intended for those whose illnesses have notresponded to traditional treatments such as chemotherapy or radiation．How do they work? We all store a specialtype of cell in our bone marrow called stem cells．These primitive cells give rise to the three types of blood cells:red, white and platelets．Everyone's stem cells have certain genetic characteristics or markers that make themunique from others．Despite this uniqueness, there are Some shared characteristics between people．This isimportant, because a patient's immune system will reject blood or organs received from someone else if they do notshare sufficient similarities．
        Family members, especially siblings, are always the first to be considered as donors, because there's a greaterchance that the genetic markers on their cells will have enough in common to prevent rejection aftertransplantation．In many cases, however, a familial match can't be found and then the search begins for anunrelated donor．These donors typically come from a pool of people who have already signed up on a donorregistry in the event that their cells match a needy recipient．
        Once the lab has verified a match between donor and recipient, the next phase starts．The patient is givenradiation or chemotherapy to kill the unhealthy cells．Healthy cells are harvested from the donor-either extractedfrom the pelvic bones or taken from the ann in a way that is similar to having blood drawn--and prepared in alaboratory．Once they're ready, they're given to the patient through a vein--the same way as one would receive ablood wansfusion．Once these transplanted donor cells get settled within the patient's bone marrow, they make thehealthy red blood ceils, white blood cells and platelets necessary to support life．
        One of the major problems currently faced by transplant centers is that while bone marrow transplants can curemore than 70 different diseases, there aren't enough donors on the registry to treat the more than 3,000 patientsawaiting transplants．The National Marrow Donor Program, the largest registry in the country, has approximately4．8 million adult volunteer donors, but that isn't nearly enough for the thousands who need transplants．
        Why isn't a pool of more than 4 million donors isn't enough to cover 3,000 needy patients? Here's the reason:in the vast majority of cases, finding a suitable match isn't easy．Because we are unique individuals with a varietyof ancestral backgrounds and integration patterns, finding someone similar to us is a major task．In the end, itcomes down to a numbers game--the more potential donors listed on the registry, the greater a chance of finding amatch, especially for those with unusual genetic characteristics．

The shared genetic characteristic of stem cells is important in bone marrow transplant became __

A．the same primitive cells can produce the same type of blood cells
B．one's immune system will reject the blood or organ of different genetic markers
C．one's immune system will not function well when facing different stem cells
D．the uniqueness of genetic characteristics will destroy the patient's immune system

参考答案B

解析:【结构分析】
第一段提出问题：由于登记自愿捐赠骨髓的人数还不够多，不能使所有病人都能得到与自己相匹配的骨髓做移植。
第二段指出，当传统的治疗如化学疗法或放射疗法不能奏效时，骨髓或干细胞移植通常是这类病人最后的救命之招。
第三段指出．为防止出现移植后的排异现象，家庭成员，特别是兄弟姐妹，是骨髓移植的首选捐赠者。
第四段介绍了骨髓移植的整个过程。
第五段指出，尽管骨髓移植能治疗70多种疾病，但许多移植中心面临的主要问题之一是，相对于3000多位等待移植的患者，却没有足够的注册捐赠者。
文章最后以提问的方式结束：为什么400多万的捐髓者还不能满足3000位病人的需要?这是因为在大多数情况下。要找到适合自己的骨髓是十分不易的。
【试题解析】
B。本题的出题点在因果关系处(because…)。根据题干信息词shared genetic characteristic和important，将答案锁定在文章第二段。第二段介绍了人类干细胞的独特性(uniqueness)，指出每个人的干细胞都有特定的遗传特征和标记。但是除此之外，它们还具有一些共性(shared characteristics)，本段最后一句说道，“This is important，because a patient's immune system will reject blood or organs received from someone else ifthev do not share sufficient similarities．”，即该共性尤其重要，因为如果不充分具备这种相似性，病人的免疫系统将会排斥移人体内的血液或器官。可见B正确。

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单选题 Who are usually considered the best donors for bone marrow transplant?

A．Parents．
B．Brothers and sisters．
C．Registered donors．
D．Healthy donors．

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单选题 What should be done immediately after the matched donor has been found?

A．Unhealthy cells of the patient are killed through radiation or chemotherapy．
B．Healthy cells are extracted from the donor．
C．Extracted cells are prepared in the laboratory．
D．The donor's cells are transplanted to the patient．

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单选题 The healthy cells of donors will be transplanted to the patient through __

A．pelvic bones
B．arms
C．vein
D．artery

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